Theresa May has appointed Gavin Barwell, the Croydon Central MP who lost his seat to Labour in the general election, as her new chief of staff.
Mr Barwell had clung on to his seat with a tiny 165-vote majority in 2015, but lost out to Sarah Jones on Thursday night by more than 5,000 votes.
The ex-housing minister had written a book about how to win a marginal parliamentary seat.
He replaces Nick Timothy and Fiona Hill, the double act who had been the Prime Minister's closest advisers.
Ms May is spending her weekend attempting to rebuild her top team and form a government.
Of Mr Barwell, she said: "He has been a first-class minister and is widely respected. He will bring considerable experience of the party to the post.
"As I said yesterday, I want to reflect on the election and why it did not deliver the result I hoped for. Gavin will have an important role to play in that. I look forward to working with him."
On Friday Number 10 confirmed the big five Cabinet posts would remain unshuffled.
Chancellor Philip Hammond, Home Secretary Amber Rudd, Foreign Secretary Boris Johnson, Defence Secretary Michael Fallon and Brexit Secretary David Davis will keep their jobs.
Ms May is also trying to determine how her party will work with the socially-conservative DUP in order to gain leverage in Parliament.
It is understood that Government Chief Whip Gavin Williamson, who has been dispatched to Belfast for talks, may be offering the chance of a formal coalition to the DUP, meaning its MPs could be present in the Cabinet.
Ms May has faced criticism for seeking to ally herself with "our friends in the DUP" because of the Northern Irish party's performance on issues like LGBT rights, abortion and climate change.
