She has been appointed secretary of state for international development, overseeing and scrutinising the way in which UK taxpayers’ money aids those oversees.
It comes just two months after she was made minister for the Armed Forces, having previously held the position of parliamentary under-secretary of state for defence.
Mrs Trevelyan, who supported Mr Johnson in his leadership campaign last summer, said: “I am delighted to be appointed international development secretary for this government, which has committed to invest 0.7 per cent of our income on development.
“I know from my previous role as Armed Forces minister how UK aid, alongside our world class defence and diplomacy, supports peace and prosperity around the world.
“As international development secretary I will ensure that UK aid promotes girls’ education around the world, tackles climate change, works to end preventable deaths and helps countries receiving aid become self-sufficient.
“I want to show the British public we are delivering the best results for their aid, transforming the lives of the world’s poorest and most vulnerable people, while promoting Britain’s economic and security interests.”
Elsewhere, Sajid Javid resigned as chancellor and is replaced by Rishi Sunak, chief secretary to the treasury.
Northern Ireland secretary Julian Smith is replaced by Brandon Lewis, business secretary Andrea Leadsom is replaced by Alok Sharma, housing minister Esther McVey is replaced by Robert Jenrick, environment secretary Theresa Villiers is replaced by George Eustice, culture secretary Baroness Morgan is replaced by Oliver Dowden and attorney general Geoffrey Cox is replaced by Suella Braverman.
Cabinet members remaining in place include Home Secretary Priti Patel; Foreign Secretary Dominic Raab; Cabinet Office minister Michael Gove; Health Secretary Matt Hancock; International Trade Secretary Liz Truss; Transport Secretary Grant Shapps; Defence Secretary Ben Wallace; Leader of the House Jacob Rees-Mogg; and Chief Whip Mark Spencer.
Mrs Trevelyan increased her majority to nearly 15,000 in December’s election, securing 23,947 votes to retain the seat for the Conservatives.
She was first elected in 2015 with a majority of 4,914. She increased her majority to 11,781 in 2017.