Trevelyan, who was appointed transport secretary by former prime minister Liz Truss, will now serve as a minister for the FCDO.
She said via Twitter: "Honoured to be asked by the prime minister to serve in the [FCDO] as one of his ministers. I am excited to have the opportunity to continue to champion our UK values and partnerships with friends and allies across the globe."
The new prime minister also removed Kevin Foster as transport minister, who will continue as a backbencher and MP for Torbay.
