A leadership election is a political contest held in various countries by which the members of a political party determine who will be the leader of their party.

Generally, any political party can determine its own rules governing how and when a leadership election is to be held for that party. In the United Kingdom, for example:

Leadership elections are generally caused by the death or resignation of the incumbent (that is, the person already holding the post), although there are also formal and informal methods to remove a party's leader and thus trigger an election contest to find a replacement. There is, however, no common procedure whereby the main parties choose their leader.^[1]

A leadership election may be required at intervals set by party rules, or it may be held in response to a certain proportion of those eligible to vote expressing a lack of confidence in the current leadership. In the UK Conservative Party, for example, "a leadership election can be triggered by a vote of no confidence by Conservative MPs in their current leader".^[2]

Strictly speaking, a leadership election is a completely internal affair. An intra-party election held to select its candidates for external offices, such as a president, governor, prime minister or member of a legislature is called a primary election.

Leadership elections have great importance in parliamentary systems, where the chief executive (e.g.: a Prime Minister) derives their mandate from a parliamentary majority and the party's internal leaders hold frontbench positions within the parliament, if not outright serving in a ministerial post – whether as Prime Minister in the case of the leading government party, or another Ministerial post for junior coalition partners. For that reason, most parliamentary systems do not hold dedicated Prime Ministerial primaries at all, but simply select their internal leader as their candidate for Prime Minister.

However, leadership elections are often similar to primary elections in that in the vast majority of instances, a party's leader will become prime minister (in a federal election) or premier/chief minister/first minister (in a province, state, territory, or other first-level administrative subdivision) should their party enter government with the most seats. Thus, a leadership election is also often considered to be one for the party's de facto candidate for prime minister or premier/chief minister/first minister, just as a primary is one for a party's candidate for president.

An electoral alliance, which is composed of multiple parties each with its own separate leader and organs, may also hold a common Prime Ministerial primary as in the 2021 Hungarian opposition primary, or a single party may wish to retain its leader but select someone else as its Prime Ministerial candidate, as the Portuguese Socialist Party has done in 2014.

In presidential and semi-presidential systems, the chief executive (the President) can only be removed by an impeachment procedure, which can only be initiated in specific situations and by a special procedure (typically involving a legislative supermajority, an investigation by a constitutional court, or both), and removal entails either a snap election or automatic succession to office by a Vice president. As a result, leadership elections are largely background events, as the ruling party's policies are determined by the President, not by the party's internal leader. However, some systems allow one person to serve as both the President and the leader of the ruling party simultaneously, or even mandate it (such as the Democratic Progressive Party in Taiwan).

However, this is not entirely comparable to the parliamentary situation, as the majority and minority leaders of political parties in presidential systems are not the chief executive of their country (as a prime minister would be), but are rather officers of the legislative branch of their country, a position similar to the floor leader (which similarly is a post subservient to the prime minister) of a political party in a parliamentary system which likewise doesn't hold mass enfranchised elections for such a post.