Stephen Barclay has been confirmed as the new Brexit Secretary as Theresa May seeks to fill posts in her cabinet, and Amber Rudd has returned to the cabinet.
Mr Barclay, a MP for North East Cambridgeshire and Leave supporter, had been serving as a minister at the department for health and social care.
He replaces Dominic Raab, who resigned on Thursday over Mrs May's withdrawal agreement for Brexit.
A spokesman for No 10 indicated that Mr Barclay would focus on the domestic preparations rather than negotiations.
The announcement comes after Amber Rudd was named the new work and pensions secretary - replacing Esther McVey, who also resigned over the PM's Brexit plans on Thursday.
Ms Rudd said she was "delighted" to be given the role, and saw it as her job to "try to iron out" the issues with Universal Credit.
Stephen Hammond will take over from Mr Barclay at the department for health and social care.
The government also announced replacements for two junior ministers who resigned over Mrs May's deal.
John Penrose will join the Northern Ireland office, replacing Shailesh Vara, and Kwasi Kwarteng will go to the Department for Exiting the EU, replacing Suella Braverman.
Mr Barclay - a former banker - has also held the posts of City minister and a whip at the Treasury.
BBC assistant political editor Norman Smith said he was not a household name and it was a big promotion for him.
But he also described Mr Barclay as ultra-loyal, having never rebelled against the government.
Environment Secretary Michael Gove is understood to have turned down the role of Brexit secretary following Mr Raab's departure.
Mr Barclay becomes the third Brexit Secretary since the role was created, after Mr Raab and David Davis - who resigned over Mrs May's Brexit plans in July.
He has been congratulated on Twitter by Chief Secretary to the Treasury Liz Truss, who said he was "a star" when he worked in her department.
Mrs May agreed a draft withdrawal agreement for Brexit with her cabinet on Wednesday, which had already been signed off by negotiators from both the UK and EU.
But it led to a backlash from some Brexit-supporting MPs, including Mr Raab and Ms McVey.
Around 20 Tory MPs have publicly called for a vote of no confidence in the prime minister, with more thought to have written to the chairman of the backbench 1922 Committee to call for a vote on her leadership.
But Mrs May responded to critics saying she will stay in No 10 and see the deal through.
Ms Rudd called on her colleagues to "think again" about sending letters against the PM, saying her deal was a "practical response to leaving the European Union."
She added: "This is not a time for changing our leader. This is a time for pulling together, for making sure we remember who we are here to serve, who we are here to help - the whole of the country."
Amber Rudd back in cabinet
Amber Rudd has returned to the cabinet as work and pensions secretary.
Ms Rudd, who replaces Esther McVey following her Brexit resignation, quit herself as home secretary in April amid controversy over her handling of the Windrush controversy.
She admitted having "inadvertently misled" MPs over immigration targets but a subsequent probe found she had been let down by officials.
But her appointment was met with outrage from Labour.
The party's shadow cabinet office minister Jon Trickett said: "After enforcing Theresa May's hostile environment in the Home Office, Amber Rudd will now be in charge of the DWP's hostile environment for disabled people and the poorest in society.
"With universal credit in absolute shambles, appointing a disgraced former minister who was only recently forced to resign for her role in another scandal is a desperate choice by a weak prime minister."
Ms Rudd said she had seen universal credit "transform lives" in her Hastings and Rye constituency but she "recognised there had been some issues with it".
She said she would make it her role to to "iron out those difficulties and make it a force wholly for good".
Labour MP David Lammy said her appointment so soon after the Windrush row was "wrong".
The BBC's Iain Watson said it was a huge job given the controversy surrounding universal credit, the government's flagship welfare reform.
He also said it showed Theresa May's confidence that she could appoint one of her "allies" to such a key role given the turmoil over her leadership in the past 24 hours.
Ms Rudd's return to government comes less than seven months after she faced intense criticism over the UK's treatment of the Windrush generation.
She apologised after it emerged that some migrants from Commonwealth countries, who were encouraged to settle in the UK from the late 1940s to 1973, were being wrongly declared illegal immigrants.
However, she continued to defend the hostile environment immigration policy championed by Mrs May and quit after admitting to having inadvertently misled two parliamentary committees on what she knew about targets for immigration removals.
A recent report found Home Office officials gave her the wrong information and then later failed to clear up the problem.
Ms Rudd becomes the sixth work and pensions secretary since March 2016.
A Remain supporter during the 2016 referendum, Ms Rudd has given her backing to Mrs May's draft Brexit agreement, saying it is "not perfect but perfect was never on offer".
Her return to the ministerial ranks has been welcomed by colleagues, including Sajid Javid and Liz Truss.