The award was unveiled at Crane Valley Park in west London this morning, along with a further £4 million of grants for 10 other parks in the capital.
More than 100,000 Londoners voted for the most deserving parks as part of the London mayor's Priority Parks programme.
The park receiving the £2 million boost under the Premier Park award was decided by Boris Johnson.
Representatives from CABE Space, Natural England and the London Parks & Green Spaces Forum advised the mayor on which park should receive the grant.
The Greater London Authority, London Development Agency and Groundwork London were also involved in the programme.
The 10 parks that will each receive £400,000 are:
Lordship Recreation Ground (Haringey)
Dollis Valley Green Walk (Barnet)
Mayesbrook Park (Barking and Dagenham)
Fairlop Waters Country Park (Redbridge)
Brent River Park (Ealing)
Little Wormwood Scrubs (Kensington and Chelsea)
Parish Wood Park (Bexley)
Avery Hill Park (Greenwich)
Crane Riverside Park (Richmond/Hounslow)
Wandle Park (Croydon)