The Tories are set to lose the next general election unless the party jettisons Boris Johnson, former foreign secretary, and MP for South West Surrey, Jeremy Hunt said.
Mr Hunt, who stood against the Prime Minister in 2019, said "we are not giving the British people the leadership they deserve".
But his comments provoked a furious response from Cabinet minister Nadine Dorries, who accused Mr Hunt of "duplicity" and claimed he was seeking to destabilise the country to serve his own ambitions for the top job.
Mr Hunt is viewed as a likely contender if there is another leadership contest, having made the run-off in 2019 against Mr Johnson.
He confirmed he would be voting against the Prime Minister in the confidence vote triggered by discontented Tory MPs on Monday night.
Jeremy Hunt said: "The Conservative Party must now decide if it wishes to change its leader. Because of the situation in Ukraine this was not a debate I wanted to have now but under our rules we must do that.
"Having been trusted with power, Conservative MPs know in our hearts we are not giving the British people the leadership they deserve.
"We are not offering the integrity, competence and vision necessary to unleash the enormous potential of our country.
"And because we are no longer trusted by the electorate, who know this too, we are set to lose the next general election."
In a statement on Twitter ahead of the confidence vote, he said: "Anyone who believes our country is stronger, fairer & more prosperous when led by Conservatives should reflect that the consequence of not changing will be to hand the country to others who do not share those values.
"Today's decision is change or lose. I will be voting for change."
But Culture Secretary Nadine Dorries, a Johnson loyalist, criticised former health secretary Mr Hunt's record in office and his political manoeuvring.
"Your pandemic preparation during six years as health secretary was found wanting and inadequate," she said.
"Your duplicity right now in destabilising the party and country to serve your own personal ambition, more so."
Ms Dorries, a former health minister, claimed Mr Hunt had told her he expected the Government to collapse on the back of Brexit "and you would swoop in".
"If you had been leader you'd have handed the keys of No 10 to (Jeremy) Corbyn. "You've been wrong about almost everything, you are wrong again now."
She said that Mr Hunt, whose wife is Chinese, had recommended following that country's example in dealing with the Covid-19 pandemic, with cases "removed from their homes and placed into isolation hotels for two weeks".
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out...