So far 11 candidates have announced they hope to replace him, including a number of cabinet ministers as well as backbenchers.
The candidates could be narrowed down to the final two by next Thursday, with a series of debates then to let party members decide Britain’s next Prime Minister.
But who is in the running, what do they stand for, and how much experience do they have?
The 42-year-old has been the MP for Richmond (Yorks) since 2015.
A former Chancellor who made his name during the pandemic, Mr Sunak supported Brexit but also voted three times for Theresa May’s withdrawal agreement.
Resigning to force Mr Johnson out, “Dishi Rishi” has stressed the importance of fiscal responsibility, and promised not to lie to voters with “comforting fairy tales”.
The 52-year-old has been the MP for Bromsgrove since 2010.
A former Health Secretary, Chancellor, and Home Secretary, Mr Javid supported remain but went on to defend the Brexit party.
He's promised to cut corporation tax to 15 per cent, scrap the national insurance hike, as well as offering a new £5 billion package to help with energy bills.
The 49-year-old has been the Tonbridge and Malling MP since 2015.
Holding the position of Chairman of the Foreign Affairs Committee since 2017, Mr Tugendhat has no ministerial experience and supported remain.
He's emphasised the need for a "clean start", and dismissed plans to cut corporation tax, saying it's “not realistic unless you have a 10-year economic plan”.
The 55-year-old has been the South West Surrey MP since 2005.Currently the chair of the Health and Social Care Select Committee, Mr Hunt is one of the few candidates to have been a shadow minister.A remainer who changed his mind, Mr Hunt has been the Health Secretary, Foreign Secretary, and run the department of Culture, Olympics, Media and Sport.
He has promised to remove business rate for five years, slash corporation tax to 15 per cent, and support HS2.
The 49-year-old has been the MP for Portsmouth North since 2010.
A passionate Brexiteer, Ms Mordaunt has been the Defence Secretary, Minister for International Development as well as a Women and Equalities Minister.
Though her policies remain unclear, she has stressed the Government was elected to deliver on its manifesto.
The 55-year-old has been the MP for Stratford-on-Avon since 2010.
The former education Secretary and now Chancellor supported Brexit, and helped force Mr Johnson out last week.
He's promised to cut funding for every Government department by 20 per cent to introduce tax cuts, and promised to increase defence spending.
The 46-year-old former Liberal Democrat has been the South West Norfolk MP since 2010, and supported remain.
The Foreign Secretary was previously the Minister for Women and Equalities, and served under David Cameron, Theresa May and Mr Johnson.She's promised to cut taxes "from day one", protect the Good Friday Agreement, and bring down the size of the state.
The 42-year-old has been the MP for Fareham since 2015.
Perhaps the most ardent Brexiteer running, the Attorney General has promised to scrap the Northern Ireland protocol her Government negotiated.
She's promised to abandon net zero target by 2050, leave the jurisdiction of the European Convention on Human Rights, and take a firm line on migration.
The 42-year-old has been the MP for Saffron Walden since 2017.
A Brexiteer, Mr Badenoch served as Minister of State for Local Government, Faith and Communities and Minister of State for Equalities between 2021 and 2022.
She's promised lower taxes, limited government, and also hit out at "identity politics".
Parliament’s best communicator is 53 and has been the Welwyn Hatfield MP since 2005.
A remainer, the Transport Secretary has also been the Minister for Housing and Local Government, Chairman of the Conservative Party and Minister without Portfolio.
He's said he'll bring forward the 1p income tax cut to “now”, lower taxes, and end tactical government by an often-distracted centre”.
The newly appointed Foreign Office minister is 43, and has been the MP for Gillingham and Rainham since 2010.
He voted to leave, hasn’t announced any policies, and is currently a joke among MPs who simply hadn’t heard of him.
Not the favourite, it would be fair to say.