To what extent do electoral institutions influence positions on same-sex marriage? Debates over same-sex marriage legislation have increased globally for the past 20 years, yet little research focuses on either debates in East Asia or the affect of electoral institutions. Using an original dataset on Taiwanese legislators and their public stances on same-sex marriage, this research finds that legislators elected under proportional representation (PR) are consistently more likely to support same-sex marriage laws than their counterparts elected in single-member districts (SMDs), even after controlling for partisanship. The results here not only highlight overlooked institutional influences on support, but also tie the broader literature on mixed-member systems to the growing research on same-sex marriage rights.