The adversarial nature of litigation is the most fundamental principle governing "procedural law," encompassing both civil and criminal proceedings. This principle must be observed in all judicial and quasi-judicial bodies and even during arbitration proceedings. As an intrinsic and fundamental aspect of litigation, it ensures justice, fairness, and impartiality of the adjudicator throughout the process. One of the essential characteristics of a fair trial at all stages is the guarantee of the right to equality before the court. In this regard, it must be acknowledged that each party to a dispute is entitled to be informed of the evidence and claims of the opposing party and to present their own arguments and evidence. This right exists in both Iranian and French law, although it is explicitly stated only in French law and lacks explicit legal recognition in Iranian law. Using a descriptive-analytical method, this study seeks to compare the principle of adversarial proceedings in the legal systems of both countries through the examination of their laws and regulations. It will be shown that, although the principle of adversarial litigation is primarily French, its connection to mandatory rules and internationally accepted principles makes its denial in Iranian legal systems impossible. Undoubtedly, understanding the nature and role of adversarial proceedings in the French legal system will contribute to uncovering new dimensions and less-known aspects of this principle in Iran.