Unlawful evidence in litigation is an institute that was introduced for the first time in the Civil Procedure Act by an amendment from July 2022. The new provision stipulates that the court can base its decision on unlawful evidence in litigation. In doing so, it must be guided by the balance between the severity of the violation of rights that may occur through the use of such evidence in litigation, on the one hand, and the importance of using such evidence to correctly and completely establish the factual situation, on the other hand. With such an approach, Croatian litigation moved away from the previous restrictive approach, which did not allow the use of unlawful evidence. Namely, some European jurisdictions do not allow the use of unlawful evidence in litigation at all, while some European jurisdictions, such as Croatia, allow its use in litigation. Due to such differences in regulations, the practice of the European Court of Human Rights represents a decisive source in the matter of obtaining and using unlawful evidence in litigation. Since until now unlawful evidence in litigation and the criteria for its use were not legally prescribed and therefore were poorly regulated compared to criminal proceedings, the Constitutional Court of the Republic of Croatia played the biggest role in the construction of that institute through its practice. Therefore, this paper analyzes the development of this institute in the practice of the European Court of Human Rights and in the practice of the Constitutional Court of the Republic of Croatia. At the end, a review is given of what criteria, with regard to the amendment, the Croatian courts follow when deciding on the admissibility of such evidence in civil proceedings.