But Mr Javid's resignation as Chancellor due to his reluctance to sack his political advisers has raised the question - has Number 10 now got too much power?
"It will be based in Number 10 and Number 11 (Downing Street) and will jointly advise the Prime Minister and the Chancellor of the Exchequer as they work to level up the economy across the United Kingdom", the spokesman said, adding that Sunak had worked closely with his predecessor on the budget due in March.
The PM said he had to fire all his special advisers and replace them with No 10 special advisers to make it one team.
"The chancellor said no self-respecting minister would accept those terms". "A government in chaos within weeks of an election", said John McDonnell, Labour's finance spokesman.
British finance minister Sajid Javid quits in Cabinet reshuffle
Now his Conservative administration faces the even bigger challenge of negotiating a new trading relationship with the European Union while also seeking trade deals with the United States and other countries. His office said Foreign Secretary Dominic Raab, Home Secretary Priti Patel, Justice Secretary Robert Buckland and Cabinet Office Minister Michael Gove were all staying.
Several high-profile women in Johnson's government, including Business Secretary Andrea Leadsom, Environment Secretary Theresa Villiers and Housing Minister Esther McVey, all said they had been fired.
Anne-Marie Trevelyan was promoted to minister for worldwide development, while other big departments - such as foreign, home affairs, trade and health - kept their ministers.
Besides Javid's exit, perhaps the greatest surprise in the Cabinet reshuffle is the firing of Northern Ireland Secretary Julian Smith, who had success securing a deal to end a three-year suspension of the local government.
Brandon Lewis, a former security minister, was named to replace him. The summit, known as the 26th Conference of the Parties, or COP26, is scheduled to be held in Glasgow, Scotland, in November.