The research by the government department which promotes UK businesses has put new contracts, sales and foreign investment in the last year down to the Games.
The government has estimated that the cost of hosting the games was £8.9bn.
Prime Minister David Cameron said: “This £9.9bn boost to the UK economy is a reminder to the world that, if you want the best, if you want professionalism, if you want jobs done on time and on budget then you should think British.
“With companies across the country we are harnessing the Olympic momentum and delivering the lasting business legacy of the Games that will help make Britain a winner in the global race.
“But that’s not where the good news ends. The Games are also delivering a strong social legacy.
UK Business Secretary Vince Cable defended the figures in the report following claims that the numbers had been exaggerated.
“A lot of people were very cynical about this but as a result of all the work that was done we have this very considerable amount,” said Cable. “It has been independently audited and not been plucked out of the air.”
The report also said spending from tourists in the UK for the Olympics meant that there was net economic growth of £600m to the visitor economy during Games time, excluding ticket sales.
Culture Secretary Maria Miller said: “London 2012 showed the very best of Britain and hosting the Olympic and Paralympic Games has delivered huge economic benefits to the country.
“We sat squarely on the centre of the world stage and last summer allowed us to showcase our incredible country, resulting in more growth, investment and a boost for tourism. However this is just the start, we have a 10-year legacy plan and we must continue to make the very most of the opportunities the Games gave us.”
Mayor of London Boris Johnson added: “They said we couldn’t run a bath – and we delivered the greatest Olympic and Paralympic Games the world has ever seen.
“This is only the beginning of a process that will drive extraordinary regeneration in east London. But we can already say, with pride, that the 2012 Games have made a lasting difference – for the better – to the economy of London and the UK.”
MORE: The latest football news
MORE: The latest tennis news
BIOGRAPHY: Mohamed Salah