Kwasi Kwarteng has been appointed chancellor, as Liz Truss begins to assemble her new cabinet.
He served as business secretary under Boris Johnson and is a close ally of Truss and early supporter of he leadership bid.
It follows Therese Coffey being appointed health secretary and deputy prime minister.
Truss began her cabinet reshuffle with a cull of prominent Rishi Sunak supporters, sending Dominic Raab, Grant Shapps and Steve Barclay to the backbenches swiftly after she became prime minister.
She removed the senior figures who had backed her rival in the Tory leadership race promptly after heading to her House of Commons office following her first speech in Downing Street on Tuesday.
Kwarteng, whose appointment to No 11 had been widely expected, replaces Nadhim Zahawi in the Treasury.