Michael Gove has insisted he has "evolved" as a politician since saying he was "incapable" of being Prime Minister.
The Tory leadership contender said he was now ready for the top job as the battle for Downing Street hotted up.
His comments came as the crossfire over a no-deal Brexit dominated the fight for the Tory crown after Theresa May announced her departure.
Mr Gove claimed he had gained more experience since remarking he was incapable of being PM. He told BBC Radio 4 podcast, Political Thinking with Nick Robinson: "I've changed my mind. In those three years I have been through a variety of experiences.
"I led, some people may lament this, but I led the campaign to leave the European Union and that involved going up head to head with David Cameron and others in the debate formats that we had.
"And being tested during that campaign, having had time to reflect when I was on the backbenches and then coming back into government.
"I think that I've evolved as a politician, but, obviously, we'll see in the course of the next few days and weeks who people think has what it takes."
As Tory Brexit tensions increased, Philip Hammond said talk of a renegotiation before the end of October was a "fig leaf for a policy of leaving on no-deal terms".
He told BBC1's The Andrew Marr Show: "That policy has a major flaw in it ... and that is that Parliament has voted very clearly to oppose a no-deal exit.
"A prime minister who ignores Parliament cannot expect to survive very long."
Asked if whether he would vote against the Government over no-deal withdrawal if he was a backbencher in the autumn, he said: "I would certainly not support a strategy to take us out with no deal."
On whether he would vote against the Government in a confidence motion in the circumstance of no deal, Mr Hammond said: "It's a hypothetical question because I don't know what the confidence motion is.
He added: "I'm saying this is a very difficult situation. It would challenge not just me, but many of our colleagues, and I hope we will never get to that position."
Leadership contenders Boris Johnson, Dominic Raab, Andrea Leadsom and Esther McVey have said they would be prepared to quit with no deal on October 31 if necessary.
Mr Gove said he would set out his stance on no deal in the coming days, but that he agreed with Mrs May on the need for compromise in politics.
Mr Raab said he would prefer a deal, but Britain had to show it was prepared to walk away in negotiations with the EU.
He told the BBC: "I would fight for a fairer deal in Brussels with negotiations to change the backstop arrangements, and if not I would be clear that we would leave on WTO terms in October.
"We need to go out and be absolutely resolute in the way we weren't last time. It is achievable, but it will need some goodwill on the other side too."
He added: "I will not ask for an extension. Of course, if Parliament legislates that then we would be in a difficult position."
Mr Gove's intervention in the race is likely to cause concern to current front-runner Mr Johnson.
A spectacular falling-out between the two former allies in the 2016 leadership contest helped destroy both men's chances of the top job.
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.
Additional reporting by PA
