After supporting Boris Johnson's campaign to succeed May as Conservative leader, Williamson returned to the cabinet as Secretary of State for Education in July 2019.

In July 2010, Williamson called for a new law to allow local authorities to clamp down on car boot sales that disrupted traffic flow, citing villages in his constituency as examples.

[21] In June 2011, he expressed support for postwoman Julie Roberts, who had been suspended after clinging for over a mile onto the bonnet of her post van that had been stolen.

[25] In Parliament, Williamson was a member of the Northern Ireland Affairs Select Committee and was Chair of the All Party Parliamentary Group on Motor Neurone Disease.

[26][27][28] Following David Cameron's resignation, Williamson "privately vowed" to stop the front-runner Boris Johnson from becoming Conservative Party leader.

[33] Later that month, Williamson alleged that the leader of the Labour Party, Jeremy Corbyn, in meeting a Czech diplomat (later revealed to be a spy) during the 1980s, had "betray[ed]" his country.

In response to the statement, a spokesman for Corbyn stated: "Gavin Williamson should focus on his job and not give credence to entirely false and ridiculous smears".

[38][39] Williamson's remark was quoted by the president of Ukraine, Petro Poroshenko, who posted a comment on his official Twitter account: "The Kremlin's 'chemical attack' in the UK is nothing but an encroachment on British sovereignty.

"[40] In December 2018, Williamson expressed "grave" and "very deep concerns" about the Chinese telecommunications company Huawei providing technology to upgrade Britain's services to 5G.

[41] China's Defence Ministry spokesman Wu Qian criticised Williamson's comments, saying: "The remarks just reinforced the deep-rooted ignorance, prejudice and anxiety among some British people.

"[42] On 11 February 2019, Williamson delivered the speech "Defence in Global Britain" at the Royal United Services Institute outlining the future direction of the British armed forces.

[45][46] The Mail on Sunday quoted an unnamed ally of Hammond comparing Williamson to Private Pike, a hapless character in the television sitcom Dad's Army.

[47] On 1 May 2019, Williamson was asked to resign from his position as Defence Secretary, following the leaking of confidential National Security Council information related to Huawei's potential involvement in the UK's 5G network.

Three sources told the Guardian that the leak was considered so serious Mordaunt was ready to look for a D notice to warn media that publishing the information could endanger Britain's national security.

A former government insider said senior Ministry of Defence figures believed at the time that the leak "could only have come from Gavin" and "our people's lives were put at risk by it".

[60] On 6 January 2021, Williamson announced GCSE, AS and A-Level exams would once again not go ahead for students in the academic year, being replaced with teacher assessed grades.

[68] On 17 August 2020, Ofqual and Williamson announced that the algorithm method for calculating A Level results would be abandoned, and teacher assessments would be used instead, after pressure from within the Conservative Party and the claim that they had lost the confidence of the teaching profession.

In April 2021, Williamson said that a mobile phone policy ban would be introduced in schools; he also commented that students' behaviour had become worse over the period of lockdown in January.

This comment was criticised by some parents, teachers, and headteachers, claiming that "schools already had bans in place" and that Williamson was "not focusing on important matters".

[77] It was also reported that former Conservative chairman Jake Berry had warned Rishi Sunak, the prime minister, that a complaint about Williamson had been made during a private meeting.

In one WhatsApp message, Williamson indicated his frustration that he had not received an invite to the state funeral of Elizabeth II, telling Morton "There is a price for everything", before describing her conduct as "absolutely disgusting".

[78][79] A source, reported on 4 November 2022, said Williamson had not been told by the party of the formal complaint, but that he "strongly refutes these allegations", and would be "very happy to share all communications with the former chief whip with CCHQ [Conservative Campaign Headquarters] if needed".

[87] On 9 November 2022 two more sources told The Guardian that, when he was Chief Whip, Williamson was heard joking or boasting about how his tactics affected the mental health of people he worked with.

Anne Milton told Channel 4 News that Williamson had used MPs' mental and physical health problems against them, and had collected "salacious gossip" about their "sexual preferences".

Milton said that Williamson sent her an email, responding to a female civil servant asking about a minister having to alter travel plans to attend a vote, "Always tell them to fuck off and if they have the bollocks to come and see me.

"[90] Milton accused Williamson of creating a culture of fear for Conservative MPs by using gossip over their drinking, sex lives or mental health as "leverage" to keep control.

Philip Catney, a senior politics lecturer at Keele University then described the newly-formed constituency as a safe seat, with a Conservative MP being "guaranteed a job for life".

[103] In October 2023, a man was convicted of stalking Williamson; Simon Parry, of no fixed address, had "persistently followed" the MP on two occasions earlier that year.

[106] In the 2016 Resignation Honours List of David Cameron, Williamson was put forward for a Commander of the Order of the British Empire (CBE) "for political and public service".

[108][109][110] The honour drew disapproval, with Labour's shadow education secretary Bridget Phillipson describing Williamson's record as "disgraceful" and the Liberal Democrats calling the knighthood "an insult to every child, parent and teacher who struggled through COVID against the odds".