The resignation comes just two months after Mr Johnson's sweeping election victory in December and four weeks before Mr Javid was due to deliver his first budget.
The prime minister had faced calls to "come clean" over who paid for the luxury break on the island of Mustique after Mr Ross, who Mr Johnson said was responsible, denied funding the trip.
He was immediately replaced by his 39-year-old deputy, Rishi Sunak, a former banker and Brexit supporter who is seen as close to Downing Street.
Mr Ross was one of Mr Johnson's aides in City Hall and was appointed to the Olympics organising committee.
Rishi Sunak arrives at the Treasury following the reshuffle
He said Mr Ross had "not put his hand in his pocket whatsoever and can obviously prove that - [he] most definitely did not pay anything and it was not his house".
"The prime minister said he had to fire all his special advisers and replace them with Number 10 special advisers to make it one team", the source said.
The British province had no government since Sinn Fein and the Democratic Unionist Party (DUP) fell out in January 2017 over a renewable energy scandal.
But The Times newspaper said Johnson felt "blindsided" by the deal because it includes an investigation into alleged crimes by British soldiers during decades of sectarian violence known as The Troubles.More news: Astronaut Christina Koch reunited with her dog after year in space
"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 Prime Minister, before becoming Tory leader, was forced to apologise in 2019 after not properly declaring his expenses.
The register also shows earnings Mr Johnson received a year ago before becoming PM, including more than £327,000 for seven speaking engagements, one of which was a three-hour speech where he was paid £122,899.74.
Johnson began his cabinet reshuffle by sacking his ministers for Northern Ireland, business, environment and housing, as well as his attorney general.More news: Judge grants Amazon bid to pause Pentagon's JEDI cloud contract
Boris Johnson forced the resignation of his finance minister for refusing toe the line, a sign the prime minister was tightening his control in a government reshuffle created to deliver his vision for Britain beyond Brexit.
But key figures such as finance minister Sajid Javid and foreign minister Dominic Raab are expected to stay.
After years of political turmoil over Brexit, Johnson wants to focus this year on domestic issues, including investments in police, healthcare and infrastructure.
Johnson also named former aid minister Alok Sharma as the new minister in charge of the COP 26 United Nations climate summit, which is being held in Glasgow in November. She responded with a blistering attack on his leadership, and warned that planning for the summit was "way off track".More news: Kobe Bryant honored at 2020 Oscars