Prime Minister Liz Truss has sent congratulatory message to Rishi Sunak.
This comes after Sunak was appointed Tory leader.
Speaking on Twitter, Truss wrote: ‘you have my full support.’
Ms Truss was pictured leaving 10 Downing Street by the back door earlier, shortly before she formally resigns as Prime Minister.
After Ms Truss tenders her resignation to the King, Mr Sunak will be invited to form a government by His Majesty and officially become Prime Minister.
Rishi Sunak has enjoyed the fastest journey in modern political history from starting as an MP to becoming prime minister.
He first entered the House of Commons at the 2015 general election, when he won the seat of Richmond in North Yorkshire with 51 per cent of the vote.
He held the seat at the 2017 and 2019 elections, winning an increased share of 64 per cent of the vote on both occasions.
It has taken Mr Sunak only seven years to go from being a new MP to becoming the new Prime Minister.