What determines the electoral impact of prime ministers in parliamentary elections and does the electoral impact of prime ministers systematically differ from the electoral impact of competing candidates? I study the conditioning of prime ministers’ electoral impact on individual voting behaviour across and within countries to answer these questions. I consider factors on three levels: I analyse the conditioning effect of country-level electoral rules and prime ministerial power. In addition I examine the conditioning effect of contextual factors on the election-level: election timing, economic situation and government formation. I furthermore study how the political career and personal characteristics of prime ministers may condition their electoral impact. This study expands established findings on the electoral impact of candidates’ personality in parliamentary elections and the personalisation of parliamentary democracies by taking into account previously unconsidered factors. I combine several waves of CSES data with additional data on the electoral and political context of parliamentary elections and the political careers of prime ministers into a unique comparative dataset.