Judicial Economy, Preliminary Issues and the Limits of Pathfinder Litigation: Meta Platforms Ireland Ltd v Data Protection Commissioner [2025] IEHC 631

1. Introduction

The decision in Meta Platforms Ireland Ltd v Data Protection Commissioner [2025] IEHC 631 is an ex tempore ruling of the High Court (Cahill J) on a case-management application of considerable systemic importance. Although the judgment does not decide the substantive issues of data protection law, it sets a significant precedent on:

• when and how preliminary issues of law should be tried under Order 25, rule 1 and Order 34, rule 2 of the Rules of the Superior Courts (RSC);
• the proper use and limits of “pathfinder” / test-case litigation in Irish practice;
• whether parties in one set of proceedings have any right to be heard on identical legal questions being decided in another party’s case; and
• how the courts will manage multiple overlapping appeals from decisions of the Data Protection Commission (DPC) under the Data Protection Act 2018 (DPA 2018).

The immediate context is Meta’s statutory appeal (the “Passwords Appeal”) against a major DPC enforcement decision imposing a total fine of €91 million and a reprimand following an own-volition inquiry. That decision found Meta in breach of Articles 33(1), 33(5), 5(1)(f) and 32(1) GDPR.

In a separate appeal, LinkedIn Ireland Unlimited Company v DPC (Record No. 2024/580 MCA), the High Court had already, in June 2025, fixed a three-day hearing (2 December 2025) of four preliminary issues concerning:

• the scope of the statutory right of appeal under sections 142 and 150 DPA 2018;
• the type of appeal (rehearing vs review) and standard of review applicable under those sections; and
• the extent to which new evidence and arguments may be admitted on such appeals.

These same four preliminary questions are central to Meta’s various statutory appeals and mirrored judicial reviews (nine statutory appeals in total involving Meta or related entities). The Attorney General has been joined in LinkedIn’s proceedings because constitutional and EU Charter challenges to the 2018 Act also arise.

Meta sought an order that these same four preliminary issues be tried in its Passwords Appeal, at the same time as or immediately after the LinkedIn preliminary hearing. Cahill J refused that application.

The ruling therefore addresses whether identical preliminary issues, already listed for determination as net questions of law in one appeal, should also be duplicated in a second, parallel appeal, and under what circumstances the court will allow such duplication. It also clarifies that there is no right for a litigant to be heard on common legal issues simply because they are important to that litigant’s own pending cases.

2. Summary of the Judgment

2.1 The orders sought

Meta sought three forms of relief (though it ultimately focused on the third):

1. An order under Order 25, rule 1 RSC directing the trial of four specified preliminary issues;
2. Alternatively, an order under Order 34, rule 2 RSC directing the trial of the same preliminary issues;
3. A direction that those preliminary issues be heard at the same time as, or immediately after the preliminary issues already fixed for 2 December 2025 in the LinkedIn Ireland Unlimited Company v DPC appeal.

At the hearing, Meta confirmed it was essentially pursuing only the third limb: it wanted to participate in the determination of the four preliminary legal questions already scheduled in the LinkedIn Appeal, by having the same issues formally listed in its own Passwords Appeal.

2.2 The four preliminary issues

The four proposed preliminary issues (already fixed in LinkedIn) were:

1. Whether Meta (or any appellant) is entitled to appeal the entire decision under s.142 DPA 2018, or whether some aspects can only proceed as an appeal under s.150;
2. The type of appeal provided by s.142 (e.g. full rehearing, appeal on the record, etc.) and the standard of review the High Court must apply, having regard in particular to the DPC’s role under GDPR and the Article 60 “one-stop-shop” procedure;
3. If aspects can only be appealed under s.150, whether a different standard of review applies under s.150 and, if so, what that standard is; and
4. In light of the above, whether the appellant is entitled to rely on evidence and arguments not previously advanced to the DPC, and in what circumstances and to what extent.

These questions are of profound importance to all ongoing and future statutory appeals from the DPC, as Meta stressed, including the interaction with Articles 34 and 37 of the Constitution, Article 6 ECHR, and Articles 41, 47 and 48 of the EU Charter.

2.3 Meta’s position

Meta argued that it would be unfair and inconsistent with the interests of justice for these preliminary issues—on which its nine statutory appeals and matched judicial reviews depend—to be decided in LinkedIn’s case without Meta being able to be heard. In particular:

• Meta characterised the situation as akin to “pathfinder” or test-case litigation; it argued that the court would benefit from considering the issues in more than one factual context.
• Meta placed special emphasis on an expert report from Mr Ioan Peters in the Passwords Appeal concerning whether Meta’s encryption measures for “Facebook Lite” met the “state of the art” standard in Article 32 GDPR. Meta argued that:
  • its disputes about the state of the art and the DPC’s alleged failure to assess it were crucial;
  • this report illustrated the sort of expert evidence Meta would seek to adduce on appeal;
  • this evidential context would assist the court in interpreting the nature and scope of an appeal under ss.142 and 150, especially preliminary issue 4 on admission of new evidence.
• Meta contended that preliminary issues can be decided by reference to undisputed or assumed facts, and that it was legitimate—and often desirable—to have more than one “pathfinder” case representing different factual permutations, citing Xerico v Residential Tenancies Board [2025] IECA 202.
• Meta further argued that allowing it to make submissions, and possibly adding two days to the LinkedIn hearing, was a proportionate and modest burden given the significance of the issues.

2.4 The DPC’s and State’s position

The DPC and the Attorney General strongly opposed Meta’s application. In essence, they argued:

• Meta had no right to be heard on legal issues arising in separate litigation to which it was not a party.
• The preliminary issues in LinkedIn were net questions of law, appropriately divorced from disputed facts; adding a second set of proceedings and additional factual material would undermine their character as preliminary issues.
• Duplicating the hearing of the same four questions in Meta’s case would:
  • significantly increase the costs and time burden on the court, the DPC and the State;
  • yield no corresponding gain in legal clarity, as LinkedIn’s case already raised the question of admitting expert evidence;
  • risk turning the preliminary hearing into something approaching an advisory opinion or fact-heavy mini-trial, contra the guidance in L.M. v Commissioner of An Garda Síochána [2015] 2 IR 45.
• The application was unorthodox and, if accepted, would create a disruptive precedent: any litigant with downstream interests in a legal issue might insist on parallel preliminary hearings of identical questions.
• Pathfinder or test cases are typically used where there is a large volume of similar cases and often different factual permutations; LinkedIn had not been formally designated a pathfinder, and there had been no analysis to justify a “second pathfinder” in Meta’s case.

The DPC also raised delay: Meta had issued its Passwords Appeal in October 2024 but took no steps until late July 2025, by which point the LinkedIn preliminary issues had already been fixed for hearing with detailed directions.

2.5 The Court’s decision

Cahill J refused all the reliefs sought by Meta. The core conclusions were:

• The High Court has a broad but structured discretion under Orders 25 and 34 RSC to direct preliminary issues, but that discretion is “necessarily overlaid” with the imperatives of conserving court and party resources, avoiding unnecessary duplication, and ensuring just and efficient litigation management.
• The four preliminary issues had been properly fixed for hearing in LinkedIn as “net, discrete questions of law” without material factual dispute. There was no sufficient justification—and certainly nothing “exceptional”—to warrant a second hearing of the same legal questions in Meta’s appeal.
• The court saw no demonstrated material difference in the factual matrix of the LinkedIn and Passwords Appeals that would aid the determination of the legal issues; reliance on Meta’s expert report might actually undermine the suitability of the issues for preliminary determination.
• There is no right in Irish law for a litigant to insist on being heard in other proceedings simply because those proceedings involve legal issues that will have precedential impact on its own cases.
• Although the term “pathfinder” was invoked, LinkedIn had not been designated a pathfinder case in any formal sense; the order in LinkedIn was purely one for the trial of preliminary issues, and the pathfinder analogy did not justify listing identical preliminary issues in Meta’s case.
• Even if one imported the pathfinder framework, Meta had not shown why a second pathfinder was required, nor how its case represented a distinct factual permutation warranting separate treatment.
• From a case-management standpoint, allowing two full sets of submissions from different legal teams (plus the State) on the same questions would create an onerous and unnecessary burden on the court and the parties, and risk confusion rather than clarity.
• Any delay on Meta’s part did not bar its application, but it did mean that LinkedIn’s proceedings were already well advanced and set for hearing; Meta could not now claim injustice from that sequence.

The court therefore held that it was “not appropriate or consistent with the interests of justice or the efficient and just conduct of these proceedings” to grant Meta’s motion. The preliminary issues will be determined in LinkedIn’s case in December 2025, and that determination will have the usual precedential effect for Meta’s appeals.

3. Analysis

3.1 Legal framework and context

3.1.1 Data Protection Act 2018 and GDPR

The appeals in question arise from decisions of the DPC made under sections 110 and 111 of the Data Protection Act 2018 (implementing and supplementing GDPR in Irish law) and Article 60 GDPR (the “one-stop-shop” mechanism for cross-border processing).

The judgment does not reproduce the text of sections 142 and 150 DPA 2018, but it is clear that:

• section 142 creates a statutory right of appeal to the High Court from certain decisions of the DPC (particularly those taken under the Article 60 cooperation mechanism);
• section 150 provides for a different appeal route in respect of other categories of DPC decisions.

A major unresolved issue in the data protection enforcement landscape is whether these appeals are:

• full merits appeals (rehearing on facts and law, with power to admit new evidence);
• appeals on the record (largely confined to the evidence and arguments before the DPC, but with some evaluative leeway); or
• narrow legality reviews akin to judicial review (deference to the DPC’s specialist role).

This judgment does not decide that question; rather, it determines that the question will be resolved first in LinkedIn’s appeal alone, and not in parallel in Meta’s Passwords Appeal.

3.1.2 Preliminary issues under Orders 25 and 34 RSC

Order 25, rule 1 and Order 34, rule 2 RSC give the High Court power to direct that certain questions be tried as preliminary issues. Their shared purpose, as summarised in Campion v South Tipperary County Council [2015] 1 IR 716 and cited by Cahill J, is to:

“save time and cost…when the preliminary process is compared with any other suggested method of hearing, including a full trial… Convenience will also be a consideration…”

Cahill J emphasised that these rules are “necessarily overlaid” with critical considerations of conservation of cost, time and convenience. They are a deviation from the default of a unitary trial at which all issues of fact and law are determined together.

Accordingly, preliminary issues are appropriate only where:

• they are net, discrete questions of law;
• they do not depend on disputed or complex factual findings; and
• their resolution is likely to promote efficiency relative to a full trial.

3.2 Precedents cited and their influence

3.2.1 Kalix Fund Ltd v HSBC Institutional Trust Services (Ireland) Ltd [2010] 2 IR 581

This case underpins the judgment’s approach to case management and duplication. Clarke J in Kalix affirmed that the court has an inherent jurisdiction to manage proceedings, especially where there is significant factual and legal overlap between cases. The key principle extracted by Cahill J is:

• unnecessary duplication should be avoided to ensure efficient use of court time and to minimise disproportionate expense for parties.

The court relies on Kalix to frame its discretion under Orders 25 and 34 as one that must prioritise judicial economy and efficiency. Meta’s proposal for two sequential hearings of identical legal issues in two separate appeals was incompatible with that guiding principle.

3.2.2 Campion v South Tipperary County Council [2015] 1 IR 716

Cited for the shared purpose of Orders 25 and 34, Campion reinforces that preliminary issues must lead to time and cost savings and take account of convenience. This was crucial: Meta’s proposed duplication could not credibly be said to save time or cost when compared to allowing LinkedIn’s hearing to proceed alone.

3.2.3 L.M. v Commissioner of An Garda Síochána [2015] 2 IR 45

In LM, O’Donnell J (as he then was) cautioned that courts should decline to determine preliminary issues where the issue is:

“heavily fact dependent, or [where] a possible outcome would be so contingent or qualified as to require almost a form of advisory opinion.”

Cahill J uses LM for two related points:

• To emphasise that preliminary issues must be genuinely legal and not heavily fact dependent.
• To underline that preliminary issues often produce precedents on important legal questions which inevitably affect other cases:

  “one purpose and consequence of preliminary issues can be to act as precedents on important legal questions for other cases.”

This answers Meta’s fairness argument: the fact that LinkedIn’s preliminary ruling will have precedential effect in Meta’s appeals is a feature, not a flaw, of the system of precedent and of preliminary issues practice.

3.2.4 Avoncore Ltd v Leeson Motors Ltd [2021] IEHC 163

Meta relied on Avoncore to argue that multiple related cases can be managed in a way that minimises duplication—even where more than one proceeding continues in parallel. The case concerned overlapping claims arising out of the same incident and the possibility of using one case as a de facto test case while staying another.

Cahill J accepts the general principle from McDonald J that:

“The court has a discretion to ensure that scarce court resources and the resources of parties to litigation are not inappropriately wasted by an unnecessary duplication of litigation.”

But she distinguishes Avoncore on key grounds:

• In Avoncore, the same legal teams acted in both cases, making it feasible to coordinate witnesses, expert evidence and submissions to avoid repetition.
• Here, there would be at least four distinct legal teams (Meta, LinkedIn, DPC, State) in two separate appeals, making effective coordination to avoid duplication far more difficult.

Therefore, Avoncore supports the general objective of avoiding duplication but does not support Meta’s specific proposal.

3.2.5 Xerico v Residential Tenancies Board [2025] IECA 202

Meta invoked Xerico as an example where two pathfinder cases were used for the trial of preliminary issues concerning the scope of statutory appeals from the Residential Tenancies Board (RTB).

Cahill J notes that Xerico is indeed the only example brought to her attention of pathfinder cases being used specifically to try preliminary issues. However, she finds it of “limited assistance” for several reasons:

• There is no detailed analysis in the Court of Appeal’s judgment of how or why those particular cases were selected as pathfinders.
• All RTB appeals in Xerico were brought by the same appellant with what appears to have been a common legal team; the judgment largely treats them as a single set of appeals. This is very different from separate appeals by LinkedIn and Meta.
• The judgment does not emphasise distinct factual permutations as the reason for having two pathfinders.

Consequently, Xerico does not provide a solid foundation for Meta’s argument that a second “pathfinder” hearing is needed in its own appeal.

3.2.6 Lynch v Minister for Health [2024] IEHC 712

In Lynch, Simons J explained the nature of “test cases” or “lead cases” as case-management tools, not as special cost regimes. He emphasised:

• Lead cases are selected where there is a large pool of similar cases;
• The lead case is expedited and the others are adjourned generally pending its outcome;
• The judgment in the lead case is expected to have precedential value for the others; and
• More than one lead case may be needed to represent different factual permutations.

Cahill J adopts this description, but stresses that:

• Nothing in the LinkedIn proceedings has formally designated them as a “pathfinder” or “test case”; the order is simply one fixing preliminary issues for hearing.
• The pathfinder model normally involves staying or adjourning other cases while one or a small number proceed; it does not envisage multiple sets of parallel preliminary hearings on identical legal issues.

Thus, Lynch helps to define what a pathfinder is, and—by contrast—why the present situation does not fit neatly into that model.

3.2.7 Nyembo, Duffy and Croke

Although not analysed in depth, the judgment references:

• Nyembo v Refugees Appeals Tribunal [2006] IEHC 388;
• Duffy v News Group Newspapers (No 2) [1994] 3 IR 63; and
• Croke v Waterford Crystal Ltd (High Court, Smyth J, 26 June 2003).

These authorities are cited collectively in support of the general propositions that:

• Preliminary issues must genuinely advance efficiency and not entangle the court in disputed facts; and
• The court retains a discretion to refuse to determine preliminary issues where they would not serve those purposes.

3.3 The Court’s legal reasoning

3.3.1 No factual justification for a duplicate preliminary hearing

A central plank of Meta’s argument was that its Passwords Appeal raised a distinctive factual and evidential context—especially through the expert report on encryption—which would assist the court in interpreting sections 142 and 150 DPA 2018.

Cahill J rejected this, emphasising that:

• The four preliminary issues have already been fixed in LinkedIn as pure questions of law; by definition, they must be capable of determination without diving into contestable facts.
• There was no sufficient evidence before the court to show that the factual matrix in the LinkedIn proceedings was inadequate, or that Meta’s facts would materially assist the court.
• Meta’s reliance on the expert report was in tension with the very concept of preliminary issues: the more one relies on case-specific expert evidence, the less appropriate it is to decide matters by preliminary issue.

In short, for a second set of preliminary issues to be justified, the court would have needed to see:

• a clear, concrete distinction between the facts of LinkedIn’s case and those of Meta’s Passwords Appeal;
• an explanation of why that factual difference would matter to the legal interpretation of ss.142 and 150; and
• evidence that LinkedIn’s case alone would not provide a sufficient factual platform for the legal analysis.

Meta had not provided such a showing.

3.3.2 No right to be heard in others’ litigation on shared legal issues

Meta argued that because the preliminary ruling in LinkedIn will be highly influential, fairness requires that it be heard on those questions now rather than later. Cahill J responded by grounding her analysis in two fundamental principles:

1. The doctrine of precedent: A judgment on questions of law in one case will normally bind or strongly guide future courts in other cases. That is not a procedural unfairness; it is how the common law system functions.
2. Standing and appeal rights: Only parties to litigation (or properly joined parties) have a right to be heard or to appeal. There is no free-floating entitlement for non-parties—or parties in parallel litigation—to intervene simply because a legal ruling may affect them in future.

Accordingly, statements such as Meta’s concern that “its position on the preliminary issues will not be fully determined in the LinkedIn proceedings” could not alter the basic legal reality:

• Meta is not a party to the LinkedIn Appeal.
• It has no right to appeal the outcome in LinkedIn.
• These consequences follow from the general structure of the court system, not from any special unfairness in this case.

3.3.3 Pathfinder/test-case litigation: a limited and context-specific tool

While recognising that “pathfinder” or “test” cases are a familiar case-management technique, Cahill J carefully confined their relevance:

• LinkedIn’s appeal was not chosen as a pathfinder; no stay has been placed on Meta’s appeals and there was no analysis of which cases best represented the broader pool of statutory appeals.
• Meta itself showed little commitment to the classic pathfinder model; it expressly reserved the right to raise further preliminary issues in other appeals even if these four issues were decided now.
• The usual logic of pathfinder litigation—one or a few cases proceed while others are adjourned—does not support Meta’s attempt to have two cases progress in tandem on identical preliminary questions.

Even if the pathfinder model were applicable, Meta had failed to demonstrate:

• that there were different factual permutations across the pending appeals which required more than one representative case; or
• that the Passwords Appeal and LinkedIn Appeal were materially distinct in fact and law such that both needed to be heard to provide a full spectrum of scenarios.

3.3.4 Case management and the impossibility of non-duplicative parallel hearings

A critical practical concern was how, in reality, two parallel hearings of the same four legal issues could be managed without duplication. Cahill J was not persuaded by Meta’s suggestion that careful sequencing could avoid waste, especially in light of:

• multiple separate legal teams (for Meta, LinkedIn, DPC, and the State), each likely to want to present their own distinct arguments and authorities; and
• Meta’s own affidavits stating that its arguments would be “different” from LinkedIn’s, which by definition implies additional work for the court and parties.

The judge anticipated:

• “perhaps six different sets of written and oral submissions addressing the same legal questions, but perhaps with differences of nuance and emphasis and different authorities relied upon…”
• increased complexity in trying to “disentangle, reconcile and separately determine the same identical issues in two separate cases.”

This was the very antithesis of the “save time and cost” rationale underlying Orders 25 and 34.

3.3.5 The role of delay and first-in-time

While Cahill J held that Meta’s delay was not an absolute bar to its motion, she considered it relevant to the practical justice of the situation:

• From October 2024 (when the Passwords Appeal was issued) until July 2025, Meta took no procedural steps.
• By late June 2025, the LinkedIn preliminary hearing had already been fixed for December 2025 with a detailed timetable for submissions and the involvement of the Attorney General.

This meant that by the time Meta sought to “piggyback” on that process, the LinkedIn proceedings were already well advanced toward hearing. Meta could not reasonably claim that it was unfairly excluded from a process that was already set in motion when it had not itself moved promptly to seek a similar timetable.

4. Impact and Significance

4.1 Immediate impact on data protection appeals

The most immediate consequence is procedural but highly consequential:

• The LinkedIn Appeal will go ahead in December 2025 as the sole vehicle (for now) for determining the nature and scope of appeals under sections 142 and 150 DPA 2018, including:
  • whether the High Court’s role is that of a full merits appeal court or something more limited;
  • whether the standard of review differs between s.142 and s.150; and
  • what constraints apply to new evidence and arguments on appeal.
• The outcome of that LinkedIn ruling will, by ordinary principles of precedent, structure the framework of all ongoing and future DPC appeals, including Meta’s nine statutory appeals.
• Meta will still be fully entitled to litigate how that legal framework applies to the facts of its own cases; what it cannot do is insist on being heard in LinkedIn’s preliminary hearing as a quasi-co-appellant.

4.2 Clarifying that there is no right to a “parallel preliminary hearing”

A major doctrinal clarification is that:

• A litigant does not have a procedural right to:
  • demand a second hearing of the same preliminary issues in its own case simply because those issues arise there too; or
  • participate as-of-right in another party’s litigation on the basis that common legal questions are involved.

This will be important in any area with multiple overlapping regulatory appeals—financial regulation, competition law, environmental law, etc.—where parties might otherwise attempt to secure parallel determinations of the same net legal questions.

4.3 Limits on the use of pathfinder/test-case models

The judgment also provides guidance on when and how “pathfinder” or test-case approaches can be used:

• Test cases are case-management tools that typically:
  • involve a large pool of similar cases;
  • select one (or a small number) of cases as representative;
  • adjourn or stay the others pending the outcome; and
  • rely on the precedential effect of the decision in the test case.
• They do not normally entail multiple parallel hearings of the same preliminary questions in different cases at the same time.
• Where more than one pathfinder is used (as hinted in Avoncore and Xerico), this must be justified by concrete differences in factual permutations that bear on the legal questions, not merely by a wish of different litigants to present their own arguments.

This places a clear limit on the expansion of pathfinder litigation and ensures that it remains a tool for efficiency and clarity, not a vehicle for multiplying hearings.

4.4 Strategic lessons for litigants in complex regulatory proceedings

The ruling sends several important signals to litigants, especially repeat players like large technology companies:

• Act early: If a party wishes to be the vehicle for determination of a systemic legal issue (for example, the standard of review on statutory appeal), it must move promptly to:
  • seek directions for preliminary issues in its own case; or
  • apply for formal designation of its case as a pathfinder, with appropriate stays on other proceedings.
• Expect precedent: Legal issues resolved in earlier appeals will generally bind or heavily influence later ones; the courts will not replicate preliminary issues simply because multiple parties are affected.
• Focus on distinctiveness: If a party argues that its case must also be used to determine a preliminary issue already listed elsewhere, it will have to show:
  • clear factual differences from the existing case; and
  • a compelling explanation of why those differences are material to the legal question.

5. Complex Concepts Simplified

5.1 What is a “preliminary issue”?

A preliminary issue is a question (usually of law) decided by the court before it hears the full case. The idea is:

• If the legal question is resolved one way, it may dispose of the entire case, or;
• At least, it will significantly narrow the issues, making any later trial shorter and cheaper.

Preliminary issues are appropriate where:

• the question is largely independent of disputed facts; and
• it is likely to save time and cost compared to going straight to a full hearing of all matters.

5.2 Orders 25 and 34 of the Rules of the Superior Courts

• Order 25, rule 1 allows the court to direct that any question or issue may be tried before, at, or after the trial of the main proceedings.
• Order 34, rule 2 allows the court to order a separate trial of a question of law or fact, again as a case-management measure.

Although framed slightly differently, their common goal is efficient case management. The court will always consider:

• Does a preliminary issue save time and cost, compared with hearing everything together?
• Is the issue sufficiently self-contained and not fact-heavy?
• Would splitting issues create more complexity than it resolves?

5.3 Pathfinder / test-case litigation

A pathfinder or test case is:

• One (or a few) chosen case(s) from a large group of similar cases;
• Heard first, often on an expedited basis;
• With the expectation that the judgment will have precedential or persuasive effect on the rest;
• While the other cases are stayed or adjourned to await the outcome.

Pathfinders are not a formal category in rules or statute; they are a practical device used by judges to handle mass or repeated litigation efficiently.

5.4 Standard of review on statutory appeals vs judicial review

A major live issue (to be decided in LinkedIn) is the standard of review on statutory appeals under sections 142 and 150 DPA 2018. Broadly:

• On a judicial review, the court usually asks whether the decision-maker:
  • stayed within its powers;
  • followed fair procedures; and
  • reached a decision that is not irrational.
  It does not normally re-assess the facts itself.
• On a statutory appeal, the court may have broader powers:
  • to look again at the evidence (“rehearing”);
  • to receive new evidence not put before the original decision-maker; and
  • to substitute its own decision.
  How wide these powers are depends on the statute and case law.

In this judgment, Cahill J does not decide where ss.142 and 150 sit on this spectrum; she decides only that this core question will be answered first in LinkedIn’s appeal, not Meta’s.

5.5 Doctrine of precedent and standing to appeal

Two basic principles underpin the court’s rejection of Meta’s fairness argument:

• Doctrine of precedent: Legal rulings of higher courts (and often of courts at the same level) are binding or at least highly persuasive in later cases. That is a structural feature of the legal system. A party cannot complain of unfairness simply because a legal point will be decided in another case first.
• Standing to appeal: Only parties to proceedings, or those properly joined as parties, have a right to be heard or to appeal the outcome. A person affected indirectly by a legal precedent cannot insist on participating in the earlier case.

5.6 Constitutional, ECHR and Charter references

Meta pointed to the need to interpret ss.142 and 150 DPA 2018 compatibly with:

• Articles 34 and 37 of the Irish Constitution (which govern the exercise of judicial power and the administration of justice in courts);
• Article 6 of the European Convention on Human Rights (right to a fair hearing in the determination of civil rights and obligations);
• Articles 41, 47 and 48 of the EU Charter of Fundamental Rights (good administration; right to an effective remedy and fair trial; presumption of innocence and defence rights).

These arguments concern whether the appeal mechanisms give a sufficiently robust and fair form of judicial control over DPC decisions. Cahill J does not decide these points, but they explain why the preliminary issues are legally weighty and why the Attorney General is participating in LinkedIn’s case.

6. Conclusion

This ex tempore ruling in Meta Platforms Ireland Ltd v Data Protection Commissioner is ostensibly about case management, but its implications are far-reaching.

The High Court makes clear that:

• Preliminary issues are exceptional tools to resolve net legal questions efficiently, not devices to multiply hearings or inject additional factual complexity.
• There is no general right for a litigant to be heard on important legal issues arising in other parties’ litigation, even if the outcome will have precedential impact on its own cases.
• The pathfinder/test-case model is limited and context-specific: it usually involves staying other cases, not running duplicate preliminary hearings; more than one pathfinder must be justified by materially different factual permutations, not simply differing business interests.
• The court’s discretion under Orders 25 and 34 RSC is governed by the overriding imperatives of judicial economy, efficiency, and fairness in the round, not by the desire of individual parties to be heard as often as possible.

In practical terms, LinkedIn’s appeal will now serve, in effect, as the first vehicle for clarifying the nature of appeals under sections 142 and 150 DPA 2018 and the admissibility of new evidence—crucial points for Meta and many others. Meta will have to litigate within the legal framework that emerges from that decision, challenging its application to the specific facts of its own appeals rather than contesting the preliminary questions in parallel.

The judgment is therefore an important statement of principle on the management of complex, multi-party regulatory litigation in Ireland, and a cautionary note to litigants that judicial resources are finite and must be used in a disciplined, non-duplicative way, even where very high regulatory and financial stakes are involved.