Elected to parliament for the first time in 2015, Mr Sunak has had a meteoric rise through government.
But his appointment is a sign of how Mr Johnson and his aides are using the reshuffle to reward loyalty – and stamp out dissenting voices.
The Richmond (Yorks) MP served as a junior housing minister under Theresa May before being promoted as chief secretary to the Treasury by Mr Johnson in July 2019.
As second in command at the Treasury, Mr Sunak was tasked with overseeing public spending under Mr Javid.
Despite tensions between No 10 and the Treasury, his star was clearly on the rise.
Mr Sunak was a key supporter of Mr Johnson in the Tory leadership contest, with allies of the prime minister citing his decision to throw his weight behind Mr Johnson as instrumental to winning over wavering Tory MPs.
In a sign of how highly rated he is by team Boris, he stood in for Mr Johnson during a TV debate during the election campaign and he was frequently put forward for media interviews.
The Brexiteer was a vocal advocate for leaving the EU during the referendum and backed Ms May’s Brexit deal three times in the Commons.
Mr Sunak’s mother was a pharmacist and his father was a GP. He attended Winchester College, an exclusive private school, before reading PPE at Oxford and studying for an MBA at Stanford University, California.
The 39-year-old worked for investment bank Goldman Sachs and co-founded an investment firm before entering politics.
He is married to Akshata Murthy, the daughter of Indian billionaire N R Narayana Murthy. They have two children, Krishna and Anoushka, and the family live in Kirby Sigston, outside the town of Northallerton, in Yorkshire.
On his website, Mr Sunak says his interests are “keeping fit, cricket, football and movies”.