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".

As Labour leader, Starmer focused on repositioning the party away from the left and the controversies that plagued Corbyn's leadership, with promises 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.

[13][14] He indicated he will continue with the Labour policy of scrapping tuition fees as well as pledging "common ownership" of rail, mail, energy and water companies and called for ending outsourcing in the NHS, local governments and the justice system.

[29] By 2022, Starmer had dropped most of the socialist policies he advocated during his leadership run, including pledges made to nationalise water and energy, scrap tuition fees, and defend free movement within the EU.

[30][31] Starmer responded to criticism in 2023 by stating that they remained "important statements of value and principle", but cited the COVID-19 pandemic, the Russian invasion of Ukraine and the economic crisis resulting from the 2022 mini-budget as having meant that these pledges have had to be adapted.

[34][35] In February 2023, Starmer set out five "national missions" as the basis for Labour's manifesto for the 2024 general election:[36] achieving the highest sustained growth in the G7 by the end of his first term,[37] establishing the UK as a "clean energy superpower" with zero-carbon electricity by 2030; enacting health and care reform, improving the justice system, and dismantling the barriers to opportunity" with education and childcare reforms.

[38] The report was published in 2022 and was endorsed and promoted by Starmer, and recommended the abolition of the House of Lords, extending greater powers to local councils and mayors, and deeper devolution to the countries of the United Kingdom.

[39] In November 2022, Starmer said that he would strip politicians of the power to appoint people to the House of Lords in the first term of a Labour government,[40] adding that the public's trust in the political system had been undermined by successive Conservative leaders granting peerages to "lackeys and donors".

[58] This led to speculation Corbyn could stand for election as the Mayor of London or in his current parliamentary constituency as an independent candidate, in opposition to Labour.

[87] The BBC's Laura Kuenssberg and Robert Peston of ITV News said that the reshuffle aimed to "combine experience and youth" and end "the fatuous project of trying to ... placate Labour's warring factions", and instead chose "shadow ministers for their perceived ability".

[103] In August 2022, Parliamentary Commissioner for Standards, Kathryn Stone, found that Starmer had breached the MPs' code of conduct eight times by failing to register interests on eight occasions.

Imran Ahmed of the CCDH stated, "Every time a violent extremist makes a threat of violence and gets away with it, the norms of those groups worsen, and others are driven to newer depths of behaviour.

"[115] Shortly before the Russian invasion of Ukraine in February 2022, 11 Labour backbench MPs signed a letter by the Stop the War Coalition that accused the UK government of "sabre-rattling" and said that NATO "should call a halt to its eastward expansion and commit to a new security deal for Europe which meets the needs of all states and peoples", whilst also arguing that NATO was an aggressive organisation due to military actions taken by its members outside its borders in the past.

[118] In an interview with the BBC in March 2022, Starmer was asked whether he would be hoping that MPs who backed Stop the War "won't be standing at the next election or if they do whether [he would] be fully supporting them to do so".

[120][121] Starmer instructed members of his shadow cabinet to refrain from joining picket lines;[122] some Labour MPs appeared on picket-lines including frontbenchers Kate Osborne, Paula Barker, Peter Kyle, and Navendu Mishra.

"[125] His dismissal was criticised by trade union leaders and Tarry wrote in an opinion piece for the i that "failing to join the striking rail workers on a picket line would have been an abject dereliction of duty for me as a Labour MP.

"[126][127] In April 2023, after writing an article in The Observer, former Shadow Home Secretary Diane Abbott was suspended as a Labour MP pending an investigation.

[131] Labour MP Jon Cruddas accused the party under Starmer of being right-wing, illiberal and of enacting a "witch-hunt", calling the decision regarding Lawson a "disgrace".

[132] In October 2023, Hamas launched a surprise attack on Israel that devolved into a war and a growing humanitarian crisis in the Gaza Strip and a strong case of ongoing genocide against the Palestinian people at the hands of Israeli forces.

[139] On 16 November 2023, Starmer suffered a major rebellion when 56 of his MPs (including ten frontbenchers) defied a three-line whip in voting for a Scottish National Party (SNP) motion proposed by Stephen Flynn to support an immediate ceasefire in Gaza.

[142][143][144] The Labour Party under Starmer suspended several parliamentary candidates and MPs, including Graham Jones, Andy McDonald, Azhar Ali and Kate Osamor, for allegedly making anti-Semitic comments about Israel during the Israel-Hamas war, or for describing its conduct as genocide.

[58] This led to speculation Corbyn could stand for election as the Mayor of London or in his current parliamentary constituency as an independent candidate, in opposition to Labour.

[55] In the run up to Labour's conference in September 2021, the party announced plans to reform its governance structure with changes including the return of its older electoral college which would give MPs, members and trade unions a third of the vote each in future leadership elections.

[153][152] Starmer gave up on the electoral college after it failed to gain the support of trade unions;[154] the party's executive committee agreed to send a series of more modest reforms to conference, including increasing the percentage of Labour MPs a candidate would need the support of to get on the leadership election ballot, banning the party's newest members from voting, and making it harder for members to deselect MPs.

[156][157] The Bakers, Food and Allied Workers' Union voted to end its affiliation to Labour dating back to early in the party's history, commenting that it had "travelled away from the aims and hopes of working-class organisations like ours" under Starmer's leadership.

[71][72] In October and November 2022, Starmer was accused of designing and using Labour's new selection process for parliamentary candidates to prevent Corbyn-supporting, left-wing, or disloyal prospective MPs from being able to stand at the 2024 general election.

[167] Scotland's Anas Sarwar and Wales's Mark Drakeford were said to be "frustrated" for not being consulted over the idea of imposing the process used in England on the Scottish and Welsh branches of the party.

Starmer's aides characterised the English checks as being used to weed out candidates who may be unsuitable to stand for parliament or who may risk damaging the party's reputation.

Labour entered the general election with a large lead over the Conservatives in opinion polls, and the potential scale of the party's victory was a topic of discussion during the campaign period.

[183] The manifesto also pledged to give votes to 16 year olds, reform the House of Lords, and to tax private schools, with money generated going into improving state education.