This article investigates the incumbency effects in Canadian federal elections, examining how the 1972 amendments to the Canadian Election Act reshaped electoral dynamics. Using a Regression Discontinuity Design, I analyze the impact of incumbency on winning probabilities and vote shares from 1867 to 2021, with a focus on the periods before and after 1972. The findings show that incumbents have a 10-percentage-point higher probability of winning compared to non-incumbents. While incumbents, particularly from the Liberal and Conservative parties, enjoy significant advantages before 1972, this effect weakens afterwards, indicating a shift toward greater party influence in electoral outcomes.

Electoral systems determine the role that representatives’ party affiliations play in political representation. According to conventional expectations, party affiliation drives the behavior of representatives when they are elected under a proportional system, while majoritarian systems mute the role of party affiliation by forcing politicians to converge to the median position of their constituency. This study directly tests these predictions within a common party system by matching referenda decisions of constituents with voting behavior of their representatives who are elected either under a majoritarian or proportional system.