An interim leader, in Canadian politics, is a party leader who is appointed by the party's legislative caucus or the party's executive to temporarily act as leader when there is a gap between the resignation or death of a party leader and the election of his or her formal successor.

Usually a party leader retains the leadership until his or her successor takes over; however, in some situations this is not possible. This may be because the leader passes away (eg. Wilfrid Laurier), or because a leader is forced to resign due to controversy or scandal before a convention can be organized (eg. Glen Clark), because a leader is forced to recontest his or her leadership (eg. Joe Clark, Stockwell Day), or because a new party is incorporated from existing party caucuses (eg. Canadian Alliance, Conservative Party of Canada). Sometimes an outgoing leader decides to resign immediately in order to ensure party unity, because he or she has accepted an appointment or been elected to another position (such as in the case of Jean Charest who resigned as Progressive Conservative leader to contest the leadership of the Liberal Party of Quebec), or they have lost their seat in a general election and are unable or unwilling to attempt to contest a by-election. When a sudden vacancy occurs an interim leader is appointed by the party's caucus or the party executive.

By convention, an interim leader should be a caucus member who is not standing as a candidate in the official leadership race, so that he or she does not gain unfair advantage in the leadership contest. However, an interim leader may occasionally stand in the subsequent leadership race. This is particularly the case where it is recognized in advance they will likely be acclaimed or very widely supported for the full party leadership. Raj Pannu became interim leader, then was acclaimed leader, of the Alberta New Democrats following the resignation of Pam Barrett in 2000.

An interim leader has all the rights and responsibilities of an elected party leader, except that he or she does not have the discretion to call a leadership race, as one must be held within a certain time period after an interim leader is appointed.

An interim leader may, if necessary, lead the party into an election, but by Canadian custom, an election is usually not called while one of the parties is in a leadership race.

Interim leaders in Canadian politics have included:

• Daniel Duncan McKenzie (Liberal Party of Canada) - 1919, between the death of Wilfrid Laurier and the election of William Lyon Mackenzie King
• Thomas Kennedy (Progressive Conservative Party of Ontario) - 1948-1949, between the resignation of George Drew to contest the leadership of the federal Progressive Conservatives and the election of Leslie Frost
• Erik Nielsen (Progressive Conservative Party of Canada) - 1983, between the resignation of Joe Clark to run in a leadership convention after being unsatisfied with the results of a leadership review and the election of Brian Mulroney
• Elsie Wayne (Progressive Conservative Party of Canada) - 1998, between the resignation of Jean Charest to seek the leadership of the Quebec Liberal Party and the re-election of Clark.
• John Lynch-Staunton (Conservative Party of Canada) - 2003-2004, between the incorporation of the new party and the election of Stephen Harper
• Deborah Grey (Canadian Alliance) - 2000, between the incorporation of the new party and the election of Stockwell Day
• John Reynolds (Canadian Alliance) - 2001-2002, between the resignation of Day and the election of Stephen Harper
• Andy Brandt (Progressive Conservative Party of Ontario) - 1988-1990, between the resignation of Larry Grossman (who lost his seat in the 1987 Ontario election) and the election of Mike Harris
• Dan Miller (New Democratic Party of British Columbia) - 2000, between the resignation of Glen Clark who had been criminally charged and the election of Ujjal Dosanjh (Miller also served as interim premier as the NDP was in government at this time)
• Joy MacPhail (New Democratic Party of British Columbia) - 2001 - 2003, between the party's 2001 election defeat (in which Dosanjh lost his seat) and the election of Carole James