Boris Johnson has replaced Amber Rudd only hours after she stunned Westminster by quitting the Cabinet and the Tory Party.
Therese Coffey MP, an environment minister and MP for Suffolk Coastal, has been promoted to Work and Pensions Secretary.
Elected in 2010, Ms Coffey is a former deputy Commons leader and was appointed as environment minister by Theresa May.
Her predecessor Ms Rudd resigned after suggesting the Government was aiming to take the UK out of the EU without a deal.
Speaking on the BBC’s Andrew Marr Show, the Hastings & Rye MP said the PM failed to satisfy her that the Government was doing enough to negotiate an agreement with Brussels.
She said: “I have not seen enough work going into actually trying to get a deal.
“When I asked Number 10 for a summary of what the plan was for actually getting a deal, I was sent a one-page summary.”
Ms Rudd has already congratulated her successor, tweeting: “Congratulations to my good friend @theresecoffey on her appointment as Secretary of State @DWP. I know she will do an excellent job in a first rate department.”
International Trade Secretary Liz Truss called it an “absolutely brilliant appointment”.
Ms Coffey, having served in the Department for Environment, Food and Rural Affairs (Defra) for the past three years, will be well-versed in Brexit and no-deal planning.
Defra is set to be one of the departments most affected by Britain’s divorce from Brussels given its close ties to EU rules on food safety standards, farming and fishing.
Before being promoted, one of her responsibilities was improving air quality after the Government was reprimanded a number of times in the courts for failing to tackle rising levels of pollution.
She will now have to get to grips with the controversial Universal Credits roll-out, a long-running Government reform which has amalgamated a host of benefits.
There have been reports of recipients being plunged into poverty after being enrolled in the scheme, with critics calling for its roll-out to be paused.
She holds up former Tory leader Margaret Thatcher as her political hero.