The GMB is a general trade union in the United Kingdom which has more than 560,000 members. Its members work in nearly all industrial sectors, in retail, security, schools, distribution, the utilities, social care, the National Health Service (NHS), ambulance service and local government.

The 2020 Labour Party leadership election was triggered after Jeremy Corbyn announced his intention to resign as the leader of the Labour Party following the party's defeat at the 2019 general election. It was won by Keir Starmer, who received 56.2 per cent of the vote on the first round. It was held alongside the 2020 Labour Party deputy leadership election, in which Angela Rayner was elected to succeed Tom Watson as deputy leader.