Short answer
Yes. Rome I expressly permits it, and permits it retrospectively:
"The parties may at any time agree to subject the contract to a law other than that which previously governed it, whether as a result of an earlier choice made under this Article or of other provisions of this Regulation. Any change in the law to be applied that is made after the conclusion of the contract shall not prejudice its formal validity under Article 11 or adversely affect the rights of third parties." —
Three points are packed into that provision.
The freedom is broad. "At any time" means during performance, during a dispute, and in principle during proceedings. It applies whether the original law came from an earlier choice or from the default rules in Articles 4 to 8.
It can operate retrospectively. The Regulation contemplates a change made after conclusion affecting the contract as a whole, which is why it needs the two safeguards that follow.
There are exactly two express safeguards. Formal validity under Article 11 cannot be prejudiced, and third-party rights cannot be adversely affected.
The general limits on choice of law continue to apply after a change, because Article 3(2) is a route back into Article 3, not an escape from it.
Safeguard one: formal validity
A contract validly concluded under the original law does not become void because the new law imposes stricter formalities.
Article 11 sets out alternative reference rules for formal validity — a contract between parties in the same country is formally valid if it satisfies the formal requirements of the law governing it in substance or of the law of the place of conclusion; where the parties are in different countries, the range of qualifying laws is wider still.
Article 3(2) preserves that position. If the contract was formally valid when made, switching to a law with a writing or notarisation requirement cannot retrospectively invalidate it.
Note the limit of the protection. It covers formal validity — the manner of conclusion. It does not protect substantive validity. If the new law treats a particular clause as unenforceable on substantive grounds, Article 11 does not save it.
Safeguard two: third-party rights
This is the safeguard that most often bites in practice, because commercial contracts rarely sit alone.
Consider who may have accrued rights referable to the original governing law:
- Guarantors and indemnifiers. A guarantee is usually calibrated to the obligations under the underlying contract as governed by a particular law. Changing that law can alter the extent of what is guaranteed.
- Assignees. Where a receivable has been assigned or pledged, the assignee's position is tied to the assigned claim. Article 14(2) makes the law governing the assigned claim determine its assignability, the relationship between assignee and debtor, and whether the debtor's obligations have been discharged. The parties to the original contract should not be able to change that by agreement between themselves.
- Security holders. Lenders taking security over contractual rights, or relying on contractual covenants, have a stake in the governing law.
- Insurers and subrogated parties. Article 15 addresses legal subrogation, and a change of law can affect the recourse analysis.
- Parties to linked contracts in a chain or network, whose own position depends on the terms of this one.
"Adversely affect" is the test, so a change that leaves a third party's position unchanged or improved is unobjectionable. But the burden of that assessment sits with the contracting parties, and the sensible course is to obtain consent rather than to assume neutrality.
The limits that do not disappear
A change of law is still a choice of law, so Article 3 applies in full.
Article 3(3). Where all other relevant elements at the time of the choice are located in one country, the choice cannot prejudice that country's non-derogable provisions. Note the wording "at the time of the choice" — for a later change, the relevant time is the time of the change, not of the original contract. A contract that has become wholly domestic in the interim cannot escape local mandatory rules by a late switch.
Article 3(4). Where all other relevant elements are located in one or more Member States, choosing a non-Member State law cannot prejudice non-derogable provisions of Union law.
Articles 6 and 8. Consumer and employment protections cannot be reduced by a change any more than by an original choice.
Article 9 and Article 21. Overriding mandatory provisions and forum public policy are unaffected.
Consent to the change
Article 3(5) provides that the existence and validity of the parties' consent to the choice of law is determined by Articles 10, 11 and 13.
Article 10(1) applies the putative law — the law that would govern if the term were valid. Article 10(2) allows a party to rely on the law of its habitual residence to establish that it did not consent, where it would not be reasonable to determine the effect of its conduct under the putative law.
This matters because a change of governing law can happen inadvertently. Article 3(1) allows a choice to be "clearly demonstrated by the terms of the contract or the circumstances of the case". A variation agreement, a renewal on new standard terms, a settlement agreement, or an amended master agreement with a different boilerplate clause can all amount to an implied change.
Parties frequently vary contracts without noticing that the new document carries a different governing-law clause from the original. Whether that effects a change of the original contract's governing law, or creates an inconsistency, is exactly the kind of dispute that is expensive and avoidable.
Consequences worth anticipating
Limitation periods move. Article 12(1)(d) places "the various ways of extinguishing obligations, and prescription and limitation of actions" within the scope of the applicable law. A change of governing law can therefore change the limitation period — potentially reviving a time-barred claim or barring a live one. Where a change is proposed during a dispute, this should be modelled before agreeing, not discovered afterwards.
Interpretation and remedies change. Article 12(1) also covers interpretation, performance, the consequences of breach including the assessment of damages within the forum's procedural powers, and the consequences of nullity. Clauses drafted for one legal system may behave differently under another — liquidated damages and penalty analysis being the classic example.
Drafting assumptions may fail. Terms drafted against one system's default rules can misfire under another. Entire-agreement clauses, good-faith obligations, notice provisions and termination mechanics are all sensitive to the background law.
Jurisdiction does not move with it. Choice-of-court agreements are excluded from Rome I by Article 1(2)(e). Changing the governing law does not change the forum, and vice versa.
Renvoi is excluded. Article 20 means the new law is applied without its private international law rules, unless the Regulation provides otherwise.
How to do it properly
- Record the change in writing, as a distinct amendment rather than buried in unrelated variations.
- State the effective date expressly, and say whether the change is retrospective or applies only from that date. Silence invites argument.
- Say what it applies to — the whole contract, or specified parts. Article 3(1) permits dépeçage, allowing the parties to select the law for part only of the contract.
- Identify affected third parties and obtain written consents from guarantors, assignees and security holders.
- Re-run Articles 3(3) and 3(4) as at the date of the change.
- Review the substantive clauses against the new law, particularly limitation, damages, termination and notices.
- Check linked documents — guarantees, security, side letters and related contracts — for consistency.
- Confirm the jurisdiction clause separately, and whether it should change too.
Conclusion
Rome I permits a change of governing law at any time, including with retrospective effect. That flexibility is genuine and occasionally very useful — in restructurings, in consolidating a group's contracts onto one system, or in settling a dispute.
The two express safeguards are narrow but real: formal validity is preserved, and third-party rights cannot be adversely affected. The larger risks are the ones Article 3(2) does not mention — that limitation periods shift under Article 12(1)(d), that the general limits in Articles 3(3) and 3(4) are reassessed as at the date of the change, and that a change can happen by accident through an inconsistent clause in a later document.
Change the governing law deliberately, in writing, with a stated effective date and third-party consents — or take care not to change it at all.
Sources
This article provides general legal information, not advice for a specific matter. Laws, facts and procedural deadlines may change the result. Follow the linked primary sources and obtain local advice before acting.