There is a long-standing debate about elections and whether they lead to democratization episodes. We contend, however, that elections can also be a hotspot for autocratization onsets. We theorize how every election is potentially contested between democratic and autocratic forces and how party systems’ polarization around this cleavage predicts autocratization onset as a result of elections. Drawing on three different datasets on democratic levels and political parties, we introduce a novel authoritarian polarization index and test its relationship with the onset of autocratization by election in 3,151 country-election-years between 1970 and 2019. We find that autocratization onset in election years is the result of (i) high authoritarian polarization; (ii) anti-pluralist ruling parties running elections without the presence of strong pluralist opposition; (iii) strong anti-pluralist political parties contesting against pluralist ruling parties. Our results are robust and stronger than alternative explanations, such as high levels of populism and affective polarization.