Sajid Javid has replaced Matt Hancock as the secretary of state for health and social care.
Downing Street announced prime minister Boris Johnson had chosen Javid, the former chancellor, to succeed Hancock who resigned earlier on Saturday evening.
Hancock quit his role after admitting breaching coronavirus rules during an alleged affair with friend and aide Gina Coladangelo.
The former minister submitted his resignation to Johnson after admitting on Friday he was “very sorry” for breaking his own department’s rules around social distancing.
"The last thing I would want is for my private life to distract attention from the single-minded focus that is leading us out of this crisis," Hancock said in a letter to the Prime Minister.
"I want to reiterate my apology for breaking the guidance, and apologise to my family and loved ones for putting them through this. I also need to be with my children at this time".
He added: "We owe it to people who have sacrificed so much in this pandemic to be honest when we have let them down as I have done by breaching the guidance".
Johnson faced intense pressure to sack Hancock after pictures emerged of him kissing Coladangelo in his departmental office.
Images leaked to The Sun and published on Friday appeared to be stills from CCTV footage captured in his Whitehall office.
They show the former health secretary in what the paper described as a "steamy clinch" with the aide on 6 May, when indoor mixing was banned.
Javid, the Conservative MP for Bromsgrove, was appointed as Chancellor of the Exchequer by Johnson when he first became Prime Minister in 2019.
However, he dramatically quit in February 2020 after Johnson asked him to fire his advisors in the Treasury and replace them with personnel chosen by Downing Street.
There was also friction between Javid and Dominic Cummings, the then chief advisor to the prime minister.
Javid has also served as home secretary, business secretary, and communities secretary. He finished fourth in the contest to replace Theresa May as Conservative party leader and prime minister in 2019.
Responding to Hancock, Johnson in a letter said: "You should leave office very proud of what you have achieved – not just in tackling the pandemic, but even before Covid-19 struck us.
“You should be immensely proud of your service. I am grateful for your support and believe that your contribution to public service is far from over.”
Adam Payne is a reporter of for CSW's sister title PoliticsHome, where a version of this story first appeared.