Mr Jenrick denied that newly-appointed Chancellor Rishi Sunak would be the PM's "puppet" after accepting terms of office that his predecessor rejected.
Karen Ward was a special advisor to former chancellor Philip Hammond during his time in Number 11 Downing Street.
Meanwhile, Salma Shah, a former adviser to Mr Javid, said it would have been "incredibly detrimental" for the former chancellor to allow Number 10 to choose his closest aides. Sunak, the son-in-law of Infosys co-founder Narayana Murthy, will join Home Secretary Priti Patel on the top government bench as the Chancellor of the Exchequer. "That does leave us vulnerable to things like an economic shock, interest rates rising".
Also sacked Thursday were Business Secretary Andrea Leadsom, Environment Secretary Theresa Villiers and and Housing Minister Esther McVey.
"Extensive preparations have already been carried out for the Budget and they will continue at pace", he said.
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.
And it was a big day for Norwich North MP Chloe Smith who becomes minister of state for the constitution and devolution.
But the finance minister's resignation - which some commentators said might have been sought by Johnson's team - because of a dispute over Javid's advisers added to the picture that the prime minister will not tolerate dissent in his government.
Brandon Lewis was appointed as Northern Ireland Secretary, while former Brexit minister Suella Braverman returned to the Government as Attorney General.
He used Thursday's reshuffle to announce Alok Sharma as his new business and energy minister, with a new responsibility for running the United Nations climate talks in Glasgow in November.
Anne-Marie Trevelyan joins the cabinet as global development secretary, having previously been a defence minister.
Oliver Dowden has become a full cabinet member as culture secretary having previously attended the meetings as paymaster general.
Today, the Prime Minister insisted to Sajid Javid that all he wanted was a Osborne/Cameron relationship but Mr Javid and his allies in the Treasury believed what was on offer from No. 10 was a very different (servant/master).
Foreign Secretary Dominic Raab, Johnson's de facto deputy Michael Gove and several other key ministers stayed in the post - and Javid was widely assumed to be safe.