Penny Mordaunt has become the first MP to throw her hat in the ring in the contest to replace Liz Truss after her dramatic resignation this week.
The leader of the Commons announced her candidacy in a tweet, saying fellow Conservatives had urged her to stand to become party leader and take the keys to Number 10.
Ms Mordaunt, who came third in the last leadership race behind Ms Truss and Rishi Sunak, wrote: “I’ve been encouraged by support from colleagues who want a fresh start, a united party and leadership in the national interest.
“I’m running to be the leader of the Conservative Party and your prime minister – to unite our country, deliver our pledges and win the next general election.”
Ms Mordaunt needs to secure the backing of at least 100 Tory MPs by Monday afternoon to stay in the race, and so far 16 MPs have publicly stated they will vote for her.
But former Chancellor Mr Sunak is also expected to launch his own bid, with 64 MPs already supporting him.
And rumours are swirling that ex-Prime Minister Boris Johnson could take another shot at the top job, with 36 offering their public endorsement so far – including three cabinet ministers.
Nominations opened on Thursday and will close at 2pm on Monday – with a leader to be chosen by the end of the week.
In the last leadership election, Ms Mordaunt won 105 nominations, behind Mr Sunak’s 137 and Ms Truss’s 113.
Ms Truss won the final round of voting among Tory party members after campaigning on a mandate to cut taxes to boost economic growth.
This ultimately proved to be her downfall after her mini-budget unleashed turmoil in the financial markets, forcing her to sack Kwasi Kwarteng as chancellor and make a series of U-turns on the economic policies that brought her into office.
Ms Truss resigned 44 days into her premiership, making her the shortest-serving prime minister in modern British history.