When do national legislatures expand LGBT+ rights? Existing explanations cite a variety of factors: changing norms and beliefs about homosexuality, equal marriage, or transgender individuals; increased representation in political institutions; the work of lobbying organizations; and social movements operating within and across borders; or more broad-based changes in attitudes among the general public. Despite notable exceptions where judicial decisions have transformed LGBT+ rights, in most established democracies, parliamentary action is a necessary prerequisite for LGBT+ rights advances. We have very little evidence, however, about what drives parliamentary success on LGBT+ rights laws: are legislators updating their preferences (conversion thesis) or is the entry of new legislators with more socially liberal policy preferences driving the change (replacement thesis)? In this paper, we test both the “conversion” and “replacement” hypotheses using a unique database of over 3000 members of parliaments across four countries with different electoral systems across four different policy areas related to LGBT+ rights. Initial findings show that incumbent members of parliament rarely change their voting behavior. Instead, legislative progress occurs via parliamentary cohort replacement which coincides with broader shifts in public opinion. However, we only find this effect among parliamentarians on the center-left of the political spectrum. Our findings not only have important implications for understanding the conditions for the advancement of LGBT+ legislation, but also contributes to the growing literature on if and why incumbent politicians’ actions are in line with their constituents demands, a key feature of any democracy.