This paper examines how partisanship and electoral autocracy (vis-à-vis democracy) influence people’s perceptions of party system polarization in their country. Although partisanship generally enhances subjective party system polarization, I posit that this relationship depends on who is in power and the nature of political regime. Cognitive dissonance between losing an election and believing that one’s party is the best motivates partisans of parties out of power to see their country’s parties as less ideologically distinct compared to partisans of governing parties. Political regimes matter too because higher stakes of political competition and skewed information environment in electoral autocracies not only encourage all citizens to see parties as more polarized, but also magnify the positive impact of partisanship—particularly co-partisanship with governing parties—on subjective party system polarization. Using individual-level data from the Comparative Study of Electoral Systems (1996–2019), the empirical analyses support these expectations, even when accounting for party system polarization based on expert party placements. These findings have important implications for scholarly debates on partisanship, electoral autocracy, and the nature of subjective electoral supply in contemporary electoral regimes. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.