The premise that parties are fundamentally motivated by office-seeking is common, but surprisingly little attention has been paid to its empirical validity. We approach this issue by analysing how parties respond to their electoral performance. Casting party leaders as the embodiment of their parties, we then examine the degree to which the length of time party leaders retain their position hinges on their party's electoral success, defined with reference both to the party's share of legislative seats and to its presence or absence in government. Our analyses centre on six parliamentary democracies in which the government is always formed by one of the two major parties either alone or in coalition with a minor party (Australia, Britain, Canada, Germany, Ireland and New Zealand) in the years from 1945 through 2000. Results indicate that party leaders' risk of removal hinges substantially on their party's seat share and/or their party's presence in government. More specifically, we find that as the seat share of both major and minor parties increases, the chance that the party leader will be removed decreases. Likewise, if a major party loses its role in government, the chance that the party leader will be removed increases dramatically. Although presence in government has no significant impact on the tenure in office of party leaders of minor parties, the magnitude of the effect is indistinguishable from that for major parties. Beyond providing strong evidence that parties are at their core motivated by electoral performance, we also estimate the magnitude of the electoral imperative, at least as it pertains to party leaders