Out-of-Court Expert Reports: Full Evidentiary Weight When Contractually Agreed

Contractually Agreed Out-of-Court Expert Investigations: The Evolving Probative Value of Reports by Experts Jointly Appointed by the Parties

In a decision dated January 8, 2026[1], the Third Civil Chamber of the Cour de Cassation held that a judge may rely exclusively on an out-of-court expert investigation where it results from a contractual agreement between the parties (as opposed to an arrangement between their attorneys within the framework of party-driven case management). Through this decision, the Cour de Cassation further blurs the line that had traditionally separated out-of-court expert investigations from court-ordered expert investigations.

 "While a judge may not base a decision exclusively on an expert report resulting from an out-of-court expert investigation — even where conducted with the participation of all parties — when it has been commissioned at the request of a single party, the situation is different where the expert investigation has been carried out pursuant to a contract entered into by the parties and conducted by an expert jointly appointed by them.”

 Through this holding, the Cour de Cassation redefines the contours of the probative value of out-of-court expert investigations.

 Court-ordered expert investigations, governed by Articles 232 et seq. of the French Code of Civil Procedure, are conducted under the authority of the judge. They are subject to a strict procedural framework designed to ensure full compliance with the adversarial principle. The expert, appointed by the court through a reasoned order, is selected from a list maintained by a court of appeals. An advance deposit is required to secure the expert’s fees. The judge retains control over the investigation throughout the entire process.

 

Court-appointed experts are subject to strict obligations[2]: they must carry out their assignment conscientiously, objectively, and impartially. Experts must refrain from making any legal conclusions, their role being strictly limited to establishing the facts. Above all, the validity of the expert investigation depends on full compliance with the adversarial principle[3]. Experts must invite the parties to all meetings and ensure that every document or technical observation is duly shared with all parties.

 

At the end of their assignment, the expert submits a report. While the judge is not bound by the expert’s findings[4] and retains full discretion, judges rarely depart from those findings in practice. To disregard the expert’s report, the judge must provide specific grounds for doing so, which effectively gives court-ordered expert investigations de facto decisive weight.

 

By contrast, out-of-court expert investigations fall outside the judge’s control. They are governed by the principle of freedom of evidence and can take two distinct forms.

 

"Traditional” out-of-court expert investigations are conducted outside any judicial proceedings, often at the initiative of a single party (unilateral expert investigations) or informally between the parties, and are based on the free choice of a technical expert. Unlike court-appointed experts, such experts are not necessarily included on a court-approved list. The absence of court supervision calls for increased vigilance. To ensure the credibility of the process, it is essential to establish a strict written framework (including the expert’s assignment, a declaration of independence, and compliance with the adversarial principle).

 

Until recently, established case law[5] held that such expert investigations, even when conducted with the participation of all parties, could not on their own suffice to convince the judge and had to be corroborated by other evidence. Unilateral out-of-court expert investigations are admissible, but cannot serve as the sole basis for a court decision.

 

The current trend, driven in particular by the Decree of July 18, 2025 and the new provisions of Articles 131 et seq. of the French Code of Civil Procedure, is to promote out-of-court expert investigations carried out by mutual agreement. Within the framework of a "participatory procedure” or a contractual agreement, the parties themselves organize expert investigations. They select the expert, determine his/her remuneration, and define his/her assignment. In this context, the rules closely align with those governing court-ordered expert investigations: the expert must be impartial, and the adversarial principle must be observed. The legislator has even provided for recourse to the judge to resolve any difficulties that may arise.

 

The applicable framework even provides that where an expert investigation is organized by agreement between the parties’ attorneys, the resulting expert report carries the same probative value as a report issued in court-ordered expert investigations. The judge may therefore rely exclusively on it to determine the facts of the case, as it has greater evidentiary weight than a traditional out-of-court expert investigation.

 

This is precisely the type of contractually agreed expert investigation that is gaining traction, as illustrated by the January 8, 2026 decision.

 

In the case at hand, the dispute arose between project owners and a project manager following the termination of a construction contract. The lower courts had held the project manager liable, relying exclusively on an expert report resulting from an out-of-court expert investigation. In the appeal before the Cour de Cassation, it was argued, on the basis of Article 16 of the French Code of Civil Procedure and Article 6(1) of the European Convention on Human Rights, that reliance on a single item of evidence infringed the right to a fair trial.

 

The Cour de Cassation dismissed the appeal, affirming the reasoning of the lower courts and carving out a notable exception to the principle that no decision may be based exclusively on a single item of evidence. The decisive criterion for the Cour de Cassation was the parties’ common intention.

  

Where an expert investigation is provided for in the contract binding the parties and carried out by a jointly appointed expert, the resulting expert report carries the same evidentiary weight as a court-ordered expert report. The judge may rely on it exclusively to rule on the dispute, without the need for additional corroborating evidence.

 

These findings suggest that the parties are ultimately bound by their own contractual foresight. By agreeing in advance to refer their technical dispute to a jointly appointed third-party expert, they are deemed to have accepted that the expert’s findings may be treated as authoritative. The safeguards of independence and compliance with the adversarial principle are deemed to be satisfied by the contractual mechanism itself.

 

This decision forms part of a broader trend aimed at enhancing the effectiveness of out-of-court expert investigations. By way of illustration, it had already been established that a judge may rely exclusively on an expert report resulting from such an investigation where the expert’s findings and conclusions relate to an established fact that is not disputed by the parties[6].

 

By granting full probative value to contractually agreed out-of-court expert investigations, the Cour de Cassation streamlines the judicial process: parties can avoid the time and cost associated with a further court-ordered expert investigation when the work has already been properly carried out at an earlier stage.

 

However, this deference to party autonomy is not absolute. The judge retains full discretionary power and remains the ultimate guardian of the right to a fair trial. The judge may still disregard an out-of-court expert report in cases of serious irregularities, a manifest breach of the adversarial principle, or a lack of impartiality on the part of the expert.

 

In the end, through this decision, the distinction is gradually fading, giving out-of-court expert investigations a probative value similar to that of court-ordered expert investigations in establishing the facts.