Keir Starmer as Leader of the Opposition

Keir Starmer served as Leader of the Opposition from April 2020, following the resignation of Jeremy Corbyn after Labour's defeat at the 2019 general election and Starmer's election as Labour leader in the ensuing leadership election, until his party won a landslide victory at the 2024 general election in July 2024. During his tenure, Starmer moved Labour toward the political centre and emphasised the elimination of antisemitism within the party. Membership of the party under Starmer's leadership has more than halved: it fell from 550,000 in 2020 to 370,000 by 2023, and continued to fall in the following years, reaching 250,000 by the end of 2025.

Having become Leader of the Opposition amid the COVID-19 pandemic, Starmer said in his acceptance speech that he would refrain from "scoring party political points" and would work with the government "in the national interest". He later became more critical of the government's response to the pandemic following the Partygate scandal. Amid the historic number of ministers resigning from Boris Johnson's government in July 2022, Starmer proposed a vote of no confidence in the government, stating that Johnson could not be allowed to remain in office given the large-scale revolt by his own ministers. Starmer also criticised Johnson's government, as well as the governments of his successors Liz Truss and Rishi Sunak, for issues such as the Chris Pincher scandal and subsequent government crisis, the economic crisis resulting from the 2022 mini-budget and subsequent government crisis, the cost of living crisis and the National Health Service strikes and other industrial disputes and strikes.

As Labour leader, Starmer focused on repositioning the party away from the left, promising of economic stability, tackling small boat crossings, cutting NHS waiting times and ''rebuilding the NHS'', worker rights enrichment, energy independence and infrastructure development, tackling crime, improving education and training, reforming public services, renationalising the railway network, and recruiting 6,500 teachers. Starmer also pledged to end antisemitism in the party. During his time in office, Starmer was accused by members of his own party of marginalising the Labour left and denying genocide in Gaza. Under his leadership, Jeremy Corbyn was expelled from the party. Labour made significant gains in the 2023 and 2024 local elections, and won a landslide victory in the 2024 general election. After Starmer became Prime Minister, he was succeeded as Leader of the Opposition by Sunak.