Boris Johnson announced he would quit as prime minister following a cascade of ministerial resignations and cabinet walkouts.
However, he has said he will remain in office until the Conservative Party are able to elect his successor – with an announcement expected in September.
Mr Sunak and Ms Truss will go head-to-head after making the final two in the Conservative voting on Wednesday 20 July.
But what are their odds to succeed Mr Johnson as prime minister? Here’s everything you need to know.
What are the latest odds on the candidates for the next leader of the Conservative party?
Rishi Sunak – 2/1
Liz Truss – 4/11
These figures are correct at the time of writing provided by Bet365.
For up-to-the-minute odds, visit the Oddschecker website.