Caruso St John Architects
, who were presented with the award on Thursday evening, converted a series of listed buildings on a London street to house the artist's private collection of work for public display.
The architects won the prestigious prize ahead of five other shortlisted contenders, including a university campus building in Glasgow and a modernist concrete house deep in the English countryside.
The original Victorian industrial buildings were former scenery painting workshops, standing alongside a railway viaduct in Vauxhall, south London.
Two entirely new spaces act as bookends to the converted row of buildings -- one featuring a spiky saw-toothed roof.
Judges described the project as "irreverent yet sensitive...a poetic juxtaposition of the old and new," in a statement issued by RIBA.
Inside, the five interconnected structures form a seamless space to accommodate exhibitions of varying scales.
"Newport Street Gallery has realized my ambition to create an unobtrusive and beautiful series of buildings that work perfectly as a space to exhibit great art," Hirst said in a statement.
"I wanted to stay true to the history and roots of the building and Caruso St John understood that from the start.
"I am immensely proud of what we achieved and the reaction it has received in its first year of opening and hope people will continue to enjoy it," he added.
The free public gallery opened last October. An exhibition of work by American artist Jeff Koons is currently on show.
It is the first time Caruso St John, who were behind the Tate Britain revamp, have won the Stirling Prize, although they were previously shortlisted in 2000 and 2006.
Of the shortlisted contenders, the Outhouse -- in Gloucestershire's Forest of Dean -- won the annual People's vote, hosted by the BBC News website
"With Newport Street Gallery ... not only has Damien opened up his enviable private art collection to the world, but he has commissioned a real work of art to house it in," said RIBA president Jane Duncan.
RIBA announced its inaugural International Prize
in May this year, featuring projects from than 20 countries. The winner will be announced in December.