While Mr Johnson is expected to win the vote, regardless of the result rebels are now actively moving to try and replace him.
But who are the favourites if the Prime Minister does lose, and what are there chances?
The chair of the Health and Social Care Select Committee was the main rival in the last Conservative leadership election, and has not given up hope.
While Brexit divided the two men then, Mr Hunt has carved out a strong reputation on Covid and confirmed on Monday he would vote against the Prime Minister.
Since being sacked by Mr Johnson as foreign secretary, his backers believe he can restore the party reputation and avoids being tainted by being part of the current cabinet.
Would be guaranteed to run, and a strong favourite.
Sacked as defence secretary when Mr Johnson became Prime Minister, Ms Mordaunt, is seen by many as a dark horse for the leadership.
MPs frequently mention her as a possible contender, and she’s been critical of the Government despite now being an international trade minister.
Ms Mordaunt has also remained critical despite her role, saying she was "shocked at the stupidity of what has taken place" in Downing Street over partygate.
Once considered the frontrunner, Mr Sunak has seen his popularity collapse with MPs and the public after a series of questionable policies and revelations.
The Chancellor was fined over partygate, raised National Insurance, then faced questions over his non-dom status.
Despite this, allies believe Mr Sunak can still turn it around.
Regularly tipped as a potential successor, Ms Truss is immensely popular with Tory members.
The Foreign Secretary is believed to play up to this, frequently being photographed in what some describe as attempts to channel Margaret Thatcher.
Having served under David Cameron, Theresa May and Mr Johnson, Ms Truss bring experience with a series of Governments.
Ms Truss has publicly supported the Prime Minister, but the no-confidence vote is crucially kept secret.
Mr Javid is widely regarded as a safe pair of hands, having been health secretary, chancellor, home secretary, housing secretary, business secretary and culture secretary.
He may also have a point to prove, having resigned in 2020 after Downing Street demanded they be able to choose his advisers.
A Thatcherite who questioned some Covid measures, Mr Javid is also popular with MPs, though struggled for support during the last leadership race.
A devout supporter of Mr Johnson, Ms Patel was saved by the Prime Minister in 2020 despite the adviser on ministerial standards finding she breached the ministerial code with bullying.
The Prime Minister overruled this, and has enjoyed her unconditional support since.
Immensely popular with the right of the party, her handling of the Home Office would deter huge swathes of more centrist Tory MPs.
The current chair of the Foreign Affairs Select Committee, Mr Tugendhat has already thrown his hat in the ring as a candidate.
A former soldier, he was deeply critical of both partygate and the Government's handling of the Afghanistan crisis.
Not a favourite, but likely to battle Mr Hunt as the “One Nation” groups candidate of choice.
Another dark horse, Mr Zahawi is seen as a strong media performer who is relatively untarnished by being part of this Government.
Fleeing Saddam Hussein with his family aged nine-years-old, his is also a wonderful story about coming to Britain as a child refugee.
You can never rule him out, and having betrayed Mr Johnson after the referendum, it would be very funny if he did it again.