Dominic Raab has been appointed Brexit Secretary by Theresa May after David Davis resigned from the government.
Mr Raab, who is currently housing minister, was a prominent Leave campaigner during the 2016 referendum.
Mr Davis quit late on Sunday night, saying Theresa May had “given away too much too easily”.
The 44-year old Mr Raab, a lawyer before becoming an MP in 2010, will now take over day-to-day negotiations with the EU’s Michel Barnier.
The MP for Esher and Walton has served in government since after the 2015 election, initially working in the Ministry of Justice before moving to the communities department in January.
Mr Davis said he could not remain in his post because he no longer believed in the plan for the UK’s future relations with the EU which was backed by the cabinet on Friday.
He said his resignation would make it easier for the UK to resist EU attempts to extract further concessions – but he insisted he was not seeking to undermine or challenge the prime minister.
In an interview with the BBC’s political editor Laura Kuenssberg, Mr Davis said Mr Raab would be “very effective” in the post.
He said he would talk to Mr Raab, who once served as his chief of staff, about the challenges he faces: “You hand over the job and tell him what the pitfalls are. That is what I will do.”
Reflecting on his resignation, he said he had lived with compromises in Brexit policy for two years but there came a point where these went “too far”.
Asked what he would say to colleagues who thought it was time to remove Theresa May, he replied it was “not a good idea” – insisting that she was a “good prime minister”.
Labour said Mr Raab’s appointment “changed nothing”.
“The deep division at the heart of the Conservative Party has broken out in public and plunged this government into crisis,” said shadow Brexit secretary Sir Keir Starmer.
“It is now clearer than ever that Theresa May does not have the authority to negotiate for Britain or deliver a Brexit deal that protects jobs and the economy.”