Penny Mordaunt has been named as the new International Development Secretary following Priti Patel's resignation on Wednesday.
Patel quit rather than be sacked by the Prime Minister over her secret meetings with Israeli officials during a family holiday in the summer.
Her exit means Theresa May has lost two Cabinet members in a week, following defence secretary Michael Fallon's resignation over sexual harassment allegations last Wednesday. He was replaced by Gavin Williamson.
Mordant, who campaigned for Brexit, had been a minister at the Department for Work and Pensions, and was the early favourite to take Ms Patel's job.
Her appointment means the Cabinet has the same gender balance as it did before, as well as the same split between MPs who backed Remain and Leave during the EU referendum.
The Portsmouth North MP previously served as minister for the Armed Forces and made headlines in 2014 when she appeared on the television show Splash!
She was also slapped down during the EU referendum by David Cameron after wrongly claiming that there was nothing Britain could do to stop Turkey joining the EU.
Downing Street also announced that Sarah Newton will replace Mordaunt as minister for disabled people, with Victoria Atkins becoming a Home Office minister - making her the first of the 2015 intake of MPs to join the Tory frontbench.
Patel had been mired in controversy since it emerged that she set up 12 meetings - including one with Israeli prime minister Benjamin Netanyahu - during her two-week trip to Israel in August.
In a major break with ministerial protocol, neither Downing Street or the Foreign Office were in advance, and May only found out about the Netanyahu meeting last Friday.
Patel was forced to apologise following a dressing-down by the prime minister on Monday, and at that point Downing Street considered the matter to be closed.
But it was then revealed that after returning from Israel, the minister had asked her officials to explore the possibility of UK aid money being given to the Israeli Defence Force for their work helping Syrian refugees in the Golan Heights. But she was told that was impossible because Britain does not recognise Israel's annexation of the area.
Her position then effectively became untenable when The Sun revealed last night that Patel had held two further meetings with Israeli ministers in September, again without informing government officials.
In her two-page resignation letter to Theresa May, Patel said her "actions were meant with the best of intentions", but admitted they "fell below the standards of transparency and openness that I have promoted and advocated".
She added: "I offer a fulsome apology to you and to the government and offer my resignation.
"I will continue to support you and the government and stand up for the Conservative values of freedom, opportunity and aspiration."
In her reply, May said Patel's meetings with the Israelis should have been done "through official channels".
She added: "Now that further details have come to light, it is right that you have decided to resign and adhere to the high standards of transparency and openness that you have advocated."
The government has also been rocked this week after a gaffe by Boris Johnson left British national Nazanin Zaghari-Ratcliffe at risk of serving five more years in an Iranian jail.
And Damian Green, the prime minister's de facto deputy, is also under investigation over claims he sexually harassed a female journalist, and that pornography was found on his work computer during a police raid in 2008. He denies both allegations.