Damian Green has been appointed First Secretary of State as Theresa May reshuffled her top team following her General Election humiliation.
Mr Green, who was previously work and pensions secretary, takes the title generally associated with the role of deputy prime minister.
A long-standing ally of Mrs May, he will also take on the role of Minister for the Cabinet Office.
Greg Clark has been confirmed by Mrs May in his position as Business, Energy and Industrial Strategy Secretary, Downing Street said.
Current Education Secretary, Justine Greening, has also entered Number 10. She did not answer when questioned on whether she is set to keep her position.
David Gauke, who was Chief Secretary to the Treasury, has been promoted to become the new Work and Pensions Secretary.
Liz Truss, who was Justice Secretary and Lord Chancellor, is the new Treasury Chief Secretary "attending Cabinet".
The move will be seen as a demotion for a minister who was widely criticised by the judiciary for failing to stand up for the judges in the face of the High Court ruling that the Government had to seek the permission of Parliament to trigger Article 50, marking the formal start of the Brexit process.
Following the news of his promotion, Mr Gauke smiled and thanked reporters as he left Number 10.