A revised plan was announced last month meaning Clapham and New Cross stations will stay open. The following ten fire stations now face closure:
Ian Lehair, Fire Brigades Union executive member for London, said:
"The cuts are dangerous and wrong, and this is devastating news for Londoners, with lives across the capital being put at risk by the Mayor's reckless cuts.
"Johnson has simply ignored the evidence, and his cuts will mean slower response times for four million Londoners.
"It's also an affront to democracy: Johnson has not listened to Londoners, his own fire authority or the elected representatives on the London Assembly."
Fiona Twycross, Labour's London Assembly fire spokesman, said:
"The Fire Authority is considering its next steps in light of the Mayor's decision today.
"Londoners have been clear about their opposition to the Mayor's closure of fire stations and we will continue to fight to keep these stations open.
"The Mayor must reconsider his position, drop his plans to close 10 fire stations and fully fund the London Fire Brigade."
Chairman of the London Fire and Emergency Planning Authority, Assembly Member James Cleverly said:
"I'm pleased that the Mayor has backed me and given his full support to the Fire Commissioner's plan. Like all fire brigades, we need to save money without compromising our ability to protect people.
"The proposals are responsible and proportionate to the significant reduction in fire risk. Labour, as always, refuse to acknowledge the need for reform and, at a time of considerable financial constraint, have insisted on increased budgets.
"The Mayor's decision means that we can finally provide clarity and stability to our firefighters, who over the last year have suffered from the prolonged uncertainty of this unnecessarily protracted process."
When he published his revised proposals last month, Mr Dobson said:
"We have to acknowledge that the number of fires we attend has gone down by half in the last 10 years, and our latest figures show that fires continued to fall at the same rate last year.
"Under my revised proposals, response times in London will remain amongst the very best of any emergency service in the UK and firefighters will continue to carry out community safety work to prevent fires at the same level as they do now.
"Fire stations and fire engines do not stop fires happening - proactive prevention work does."
London's Fire Commissioner, Ron Dobson, had originally proposed closing 12 fire stations, reducing the number of fire engines by 18 and cutting 520 jobs.
A series of public meetings and other consultations were made, resulting in changes to the original plans, but they were still rejected by the fire authority.
In a letter to the authority's chairman, James Cleverly, the Mayor said action had to be taken so that savings could be made, otherwise the authority's spending for 2014/15 would be greater than its resources.
"This eventuality would not represent sound stewardship of public funds and would place both the Mayoralty and the authority in an unacceptable position," he said.
The Mayor warned that further delays to implementing the commissioner's proposals would increase the likelihood of compulsory redundancies.
"I am also mindful of the desirability - which I know LFEPA members share - of avoiding compulsory redundancies for firefighters. Further delays to the implementation of the Commissioner's proposals will increase the likelihood of compulsory redundancies."
Mr Dobson has stressed that safety standards would not be affected by his proposals, which have been opposed by the Fire Brigades Union.
A spokesman for the London Fire Brigade said: "The authority has now received and is considering the Mayor's direction."
London's Mayor has given the go-ahead for fire station closures and hundreds of job cuts among firefighters in the capital to make savings of over £28 million over the next two years.
The fire authority had narrowly rejected the controversial proposals after Labour, the Greens and Liberal Democrats united to oppose the plans, leaving the Mayor to make a decision.
Boris Johnson has now directed the authority to implement the cuts, which will see 10 fire stations close, the number of fire engines reduced by 14, two fewer fire rescue units, 552 jobs axed and minimum crewing levels on fire rescue units reduced from five to four.
The Mayor said he wanted the plans implemented by September 16.
Boris Johnson has won the battle over the future of London's Fire Service.
The organisation in charge of the service had voted to defy the Mayor, but today it backed down in the face of his threat to take it to court.
We have this report from our Political Correspondent Simon Harris:
London's Mayor looks to have won the battle over the future of London's fire service.
The organisation in charge of the it had voted to defy the mayor but, today it backed down in the face of his threat to take it to court.
Political Correspondent Simon Harris has more.