In 2016, mayor Sadiq Khan refused planning permission for a football stadium and two blocks of flats at the Flamingo Park site in Sidcup.
The application, which proposed building a stadium for Cray Wanderers Football Club, community sports pitches and the flats, had been approved by the London Borough of Bromley.
Khan agreed with Greater London Authority (GLA) planners that "very special circumstances" did not exist to justify the development on green belt land.
The football club subsequently updated its plans and Bromley Council’s planning committee approved its revised application in March this year, against a recommendation for refusal from planners.
The application was then called in by Khan. Now he has endorsed a recommendation from GLA planners to approve the scheme.
The GLA report explains that, on their initial assessment of the application, officers considered that the club could refurbish and reuse the former clubhouse and contain the proposed stadium within previously developed land on the site, while providing the proposed residential units off-site.
But the report says that the club has subsequently successfully demonstrated that this would not be a viable option.
"The applicant has submitted alternative site layouts which demonstrate that containing the development solely within the area regarded as previously developed land is impractical in view of the specific guidelines governing the size and other requirements for football stadiums set out by the Football Association and that such an approach would also have a greater impact on the openness of green belt," the report says.
Officers advised that, on balance, the applicants had demonstrated very special circumstances to justify inappropriate development on green belt and that "the potential harm to the openness of the green belt is outweighed by the benefits to be derived from the proposal".
The benefits cited in their report include provision of new homes, community access to the new sports facilities, sporting programmes with local schools and organisations and free tickets for young people considered most in need living in Bromley and adjoining boroughs.
A spokesperson for the mayor of London said: "The mayor is delighted to have approved this application and to have secured the long-term future of this much-loved football club.
"He is particularly pleased that concerns that he raised two years ago regarding the layout of the stadium and proposed development on the green belt have been addressed. Sadiq hopes Cray Wanderers will be able to go from strength to strength now that they have moved a step closer to securing their new home."