Eight candidates are left in the race to lead the Conservative Party - and become the next prime minister - after former health secretary Sajid Javid pulled out of the contest.
To stay in the race, leadership hopefuls had to get support of at least 20 Tory MPs by Tuesday evening.
Junior minister Rehman Chishti also pulled out of the contest.
The remaining candidates are Kemi Badenoch, Suella Braverman, Jeremy Hunt, Penny Mordaunt, Rishi Sunak, Liz Truss, Tom Tugendhat and Nadhim Zahawi.
Trade Minister Ms Mordaunt is expected to launch her campaign on Wednesday morning.
The first round of voting will take place on Wednesday from 13:30 to 15:30 BST and any candidate who gets less than 30 votes from their fellow MPs will have to drop out.
Over the next few days, further votes will take place to whittle the number of candidates down to a final two.
Dropping out of the contest, Mr Javid - who helped trigger Boris Johnson's downfall when he quit the cabinet last week - said he had "set out the values and policies I think are right for the future of our great country".
"I believe the party must now look outwards, not inwards, if we are to win again.
"I look forward to seeing the debate unfold and to see colleagues working together as a united Conservative Party once the leadership election is concluded."