Environment Secretary Michael Gove has confirmed he will formally enter the Conservative leadership race.
Speaking to the Press Association from his London home, the prominent Brexiteer said he will join an already crowded field after Foreign Secretary Jeremy Hunt and ex-Cabinet ministers Dominic Raab and Andrea Leadsom threw their hats into the ring.
He said: "I can confirm that I will be putting my name forward to be prime minister of this country.
"I believe that I'm ready to unite the Conservative and Unionist Party, ready to deliver Brexit, and ready to lead this great country."
As the Tory battle for Downing Street intensifies, Mr Gove's intervention is likely to cause concern to current front-runner Boris Johnson.
A spectacular fall out between the two former allies in the 2016 leadership contest helped destroy both men's chances of the top job.
Mr Gove is posing as a self-styled "unity candidate".
Mr Hunt claimed his business background would help resolve Brexit, as the leadership tussle fired up with International Development Secretary Rory Stewart launching a strongly-worded attack on Mr Johnson.
Both Mr Raab and Mrs Leadsom have said they would be prepared to order a no-deal Brexit in October if necessary.
Mr Hunt told The Sunday Times: "If I was prime minister, I'd be the first prime minister in living memory who has been an entrepreneur by background.
"Doing deals is my bread and butter as someone who has set up their own business."
Mr Hunt's emphasis on his entrepreneurial past is being seen as swipe at Mr Johnson, who reportedly once said "f*** business" in relation to Brexit.
In a reference to mythical sea monsters, Mr Hunt said. "The real question is: who has got the experience to avoid the Scylla and Charybdis of no deal or no Brexit. I've got very important experience in that respect.
The star name will not always be the best choice. There may be times when Jiminy Cricket would make a better leader than Pinocchio.
— Rory Stewart (@RoryStewartUK) May 25, 2019
"We can never take no-deal off the table but the best way of avoiding it is to make sure you have someone who is capable of negotiating a deal."
The comments came after Mr Johnson insisted he would take the UK out of the EU on October 31 with or without a deal.
Mr Raab told the Mail on Sunday he would prefer to leave the EU with a deal, but said the UK must "calmly demonstrate unflinching resolve to leave in October – at the latest".
Mrs Leadsom, whose resignation helped trigger Mrs May's dramatic resignation statement, told The Sunday Times that if elected PM, the UK would quit the EU in October with or without a deal.
She said: "To succeed in a negotiation you have to be prepared to walk away."
Sparks began to fly in the contest with Mr Stewart saying he would refuse to serve in a government led by Mr Johnson as he appeared to compare the ex-foreign secretary to Pinocchio.
Mr Stewart was scathing about Mr Johnson's no-deal stance, insisting such a position is "damaging and dishonest".
He told the BBC: "I could not serve in a government whose policy was to push this country into a no-deal Brexit.
"I could not serve with Boris Johnson."
In a clear dig at Mr Johnson, the International Development Secretary tweeted: "The star name will not always be the best choice.
"There may be times when Jiminy Cricket would make a better leader than Pinocchio."
Health Secretary Matt Hancock said he was running for leader because the party needs to look to the future and attract younger voters.
He said he would take a different approach to try and get Commons support for a Brexit deal than the one Theresa May used.
He said: "She didn't start by levelling with people about the trade-offs.
"I think it is much, much easier to bring people together behind a proposal if you are straightforward in advance."
Meanwhile, Chief Secretary to the Treasury Liz Truss has said she will not stand for the leadership.
She told the Sunday Telegraph she will back a contender who supported Leave in the 2016 referendum.
Labour has said it will trigger a Commons no-confidence vote in the new prime minister when they take office.
The new Tory leader looks set to take over as prime minister at the end of July after Mrs May finally laid out a timetable for her exit from Downing Street.
The timetable for the contest will see nominations close in the week of June 10, with MPs involved in a series of votes to whittle down the crowded field to a final two contenders.
Tory party members will then decide who wins the run-off.