The Hammers were named preferred bidders in December but negotiations with the London Legacy Development Corporation (LLDC) have been long and tortuous.
However, the LLDC has announced that a deal has now been signed off that sees the Barclays Premier League club become anchor tenants under a 99-year lease.
Plans for the revamped stadium were unveiled yesterday, with the reported £150m facelift due to be completed in time for the 2016-17 season.
The Olympic Stadium will be transformed into a 54,000-seater venue, with the Hammers now set to embark on an independent supporter consultation process.
“It’s fantastic for everyone at West Ham United that at last all the club’s hard work over the past three years has paid off,” joint chairmen David Sullivan and David Gold said.
“Since we came to West Ham in 2010 we have had a vision to really take the club forward so West Ham United can compete on the pitch at the highest level.
“We understand the responsibilities that come with calling the nation’s iconic Olympic Stadium, which will be converted into a world-class football stadium, our new home. It is an honour we will take on with pride.”
London mayor Boris Johnson, who is also chair of the LLDC, said: “This is a truly momentous milestone for London’s spectacular Olympic Stadium ensuring its credible and sustainable future.
“Through this deal with West Ham United FC, we are defying the gloomsters who predicted this landmark would become a dusty relic.”
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