In late 2005 the Oxford-based practice beat bids from Rick Mather Architects, MacCormac Jamieson Prichard and van Heyningen and Haward to land the job on the prestigious university site.
BGS partner Alan Berman said the practice had won the competition because its submission was 'beautiful and discreet'.
The winning design boasts a double-height theatre foyer, glass gable ends - allowing views of the Kim Wilkie-designed garden - and a steel and timber roof which will 'hover' over the college's 17th-century walls.
Berman said the project would not start for at least two years, owing to a backlog of other building projects caused by the historically sensitive and congested college site - described by Pevsner as 'the grandest piece of Classical architecture in Oxford'.
'We can't do too much at the same time,' explained Berman. 'So we are doing the tricky but less sexy stuff like the kitchen and dining hall works at the moment.'