In British politics, a Lib–Lab pact is a working arrangement between the Liberal Democrats (formerly the Liberal Party) and the Labour Party.
There have been four such arrangements, and one alleged proposal, at the national level. In many local councils in the UK there are similar arrangements, although there are also arrangements where the Lib Dems and Labour oppose each other and instead form a local alliance with another party or with independent councillors.
Before the Labour Party had been formed, various candidates stood for Parliament with backing of the Liberal Party and the Labour Representation League, including Thomas Burt, Harry Broadhurst and Alexander Macdonald. These MPs were referred to as 'Lib–Lab', although there was not a formal 'pact'.
This agreement eventually fell apart with the formation of the Independent Labour Party and the Labour Representation Committee.
In 1903 an agreement was made between Herbert Gladstone (then Chief Whip of the Liberal Party) and Ramsay MacDonald (Secretary of the Labour Representation Committee) that, in thirty constituencies, the Labour Party and the Liberal Party would not stand against each other, and thus risk splitting their vote. As a result of this agreement, in contests against the Conservative party, 29 Labour MPs were returned at the general election of 1906.