Penny Mordaunt has become the latest big-name Tory to throw their weight behind leadership favourite Liz Truss.
The backing of Ms Mordaunt, who was knocked out of the race in the final round of MPs' voting, is a major coup for the Foreign Secretary.
Announcing her support in Exeter this evening, Ms Mordaunt described the frontrunner as the "hope candidate".
An estimated 160,000 Conservative Party members - around 0.3% of the UK population - are currently mulling over which candidate will become the next Prime Minister.
Voting has begun, with the winner set to be announced on September 5.
Ms Mordaunt told the audience: "I could have remained undeclared, I could be off sipping piña coladas, but I'm not. I'm here with you because this is too important and I'm not going to leave that to chance."
She said of Ms Truss: "She knows what she believes, in her resolve to stand up against tyranny and for freedom, what's what our country stands for. With her we can win."
Ms Mordaunt - who at one point a fortnight ago was ahead of Ms Truss in the race for No 10 - added: "She for me is the hope candidate."
Addressing party members, she said: “I know that choosing between them is hard but this contest is a test - a test that proceeds an even greater test.
“So who can lead, who can build that team and deliver for our country? Who does have that bold economic plan that our nation needs?
“Who understands that people need help with the cost of living now and who is going to rightly clobber our opponents?
“Who is going to hold seats and win back councils?
“Who most embodies the vision and values the British public had in their heads and their hearts when they voted in 2016 and 2019?
“I have seen enough to know the person I’m going to put my faith in and that’s Liz Truss.”
Tonight Ms Truss and Mr Sunak are locking horns at a hustings event in Exeter - but members of the public in the city said they were unimpressed with the choices on offer.
The Foreign Secretary has had a number of big endorsements by prominent MPs in recent days.
Last week cabinet member Ben Wallace - who had been tipped to stand in the days after Boris Johnson's resignation - said he was backing Ms Truss, having previously kept his cards close to his chest.
Former leadership contender Tom Tugendhat also fell in behind the leadership favourite, who polls suggest is ahead among Conservative Party members.
Earlier today her rival downplayed growing Cabinet support for Ms Truss, pointing to how he topped the ballot for MPs in the first part of the contest.
Speaking to reporters in Devon and asked if an increasing number of MPs in the Cabinet endorsing rival candidate Liz Truss is a sign that his campaign is losing momentum, Mr Sunak said: "You have to remember that actually in the parliamentary stage of this contest I topped the ballot in each and every round, with more support from MPs than any other candidate.
"And since the close of that ballot we've had lots more people coming on board as well. So actually I feel very confident that there's an enormous amount of support, in fact the most support in a parliamentary party, for my candidacy.
"But this is now about all our members, and that's why I'm going out around the country here in the south west, but absolutely everywhere, talking to members about my vision."
Earlier today voters in Exeter spoke of their disappointment at the final two.
Rachel Hartland, 72, who runs an art gallery, said: “It’s an absolute bottom of the barrel choice of people.
“I really feel that both of them have already served in the Cabinet and they have been found wanting.
“They shouldn’t be there, we should have more options."
