In a country where judicial institutions are known to be inefficient and where activists have traditionally not engaged in legal mobilization, what explains the emergence of NGO strategic litigation? The author argues that a change in the legal opportunity structure impacts how activists interact with the legal system. Comparing two states in Mexico, the author demonstrates that the introduction of private prosecution rights opened the door for activists to litigate femicide cases. The emergence of strategic litigation has helped improve compliance with international human rights law and has had a demonstration effect on how to use the law to press for accountability.