The leader of the Labour Party is the highest political office within the Labour Party of the United Kingdom. The current holder of the position is Keir Starmer, who was elected to the position on 4 April 2020, following his victory in that year's leadership election. He has served as Prime Minister of the United Kingdom since the 2024 general election.

The position of leader was officially codified in the Labour Party's constitution in 1922. Before this, from when Labour MPs were first elected at the 1906 general election and the 1922 general election (the first election that saw substantial gains for the Labour Party), the position of leader was known as Chairman of the Parliamentary Labour Party (PLP). Following the 1970 general election, the positions of party leader and PLP chair were separated.

In 1921, J. R. Clynes became the first Leader of the Labour Party to have been born in England; all leaders before him had been born in Scotland. Following the 1924 general election, Ramsay MacDonald became the first party leader to become Prime Minister of the United Kingdom, leading a minority government which lasted nine months. Following the 1945 general election, Clement Attlee became the first leader to form a majority government. In 1983, Neil Kinnock became the first party leader to have been born in Wales. The only two party leaders not to have contest general elections (excluding acting leaders) are George Lansbury, who resigned, and John Smith, who died in office.

To date, the only leaders to have led the party to victory in general elections are Clement Attlee, Harold Wilson, Tony Blair and Keir Starmer. Out of the four, Blair was the most successful, winning three consecutive electoral victories in 1997, 2001 (both landslide victories), and 2005. Wilson won four general elections out of five contested, in 1964, 1966, February 1974 (forming a minority government) and October 1974. Attlee, the first leader to lead Labour to a majority in 1945, also won in 1950. Starmer, having been elected after a poor result in 2019, led Labour to a landslide victory in 2024. Both James Callaghan and Gordon Brown also served as Prime Minister, but did not win general elections.

When the Labour Party forms the Government of the United Kingdom, the leader is expected to serve as Prime Minister, First Lord of the Treasury and Minister for the Civil Service, as well as appointing and chairing the Cabinet. Concordantly, when the party is in Opposition, the leader is expected to act as the Leader of the Opposition and to chair the Shadow Cabinet.

The Leader of the Labour Party, along with their deputy, is elected using an alternative vote system. Before 1980, the party leader was elected solely by members of the Parliamentary Labour Party (PLP).

From 1980 to 2014 an electoral college was used to elect the leader, with a third of votes allocated to the party's MPs and MEPs, a third to individual members of the Labour Party, and a third to individual members of all affiliated organisations, including socialist societies and trade unions.

Beginning with the 2015 leadership election, the party now uses a "one member, one vote" system, in which the votes of MPs, party members and members of affiliated organisations are all weighted equally. While the votes of Labour MPs are no longer counted separately, leadership candidates must first receive the nomination of at least 20% of MPs in order to appear on the ballot.