Two further rounds of voting at Westminster will follow, on 9-10 October, to determine the final two contenders.
Assuming no one pulls out and two candidates remain, Conservative members will cast their vote between 15 October and 31 October to decide the winner.
They will make their choice via secure online voting, though this system has previously been criticised for its susceptibility to hackers and rogue state interference.
In recent years, party members have tended to pick the more right-wing candidate of the final two. In the first of two leadership elections in 2022, Mr Sunak consistently won more support from MPs than Liz Truss during each round before party members ultimately chose Ms Truss.
To be eligible to vote, party members must have been active for 90 days before the ballot closes and must have been party members when nominations opened.
The new leader of the Conservative Party will be announced on 2 November – at which point Mr Sunak will hand over the reins.
The winner will become the official leader of the opposition and the figurehead of the Conservatives’ efforts to rebuild the party.
