The Tate Modern's proposals to build a £215m extension have received a £50m boost from the government.
The Tate Modern hopes to complete the glass building by 2012
The investment from the Department of Culture, Media and Sport will help fund the 11-floor building, to be built on the south side of the London gallery.
Tate director Nicholas Serota called the grant "an important endorsement by government of the contribution that the arts make to society as a whole".
It is hoped the extension will open in time for the 2012 Olympics in London.
The scheme has already received £7m from the London Development Authority and a £5m donation from banker John Studzinski.
The development, designed by Swiss architects Herzog and de Meuron, will provide more space for the Tate's collection and help reduce overcrowding.
The 23,000 square metres of space will include areas for contemporary art, several galleries and two performance zones.
The glass construction will be built on the site of the former power station's oil tanks and will require the relocation of an electricity sub-station.
The £50m investment represents the government's largest capital commitment to a cultural project since the British Library, which opened in 1998.