The Milsom Place project will see the existing Octagon chapel building and the surrounding yards transformed into 28 new shops and four restaurants.
The scheme involves the demolition of a number of 1980s buildings, the construction of a new 'raised walkway' and the opening up of a new public route from Milsom Street to Broad Street via the existing Shires Yard and Moon & Sixpence Yard.
Working for developer The L & R Group, the practice spent more than two years in discussions with planning officers and the historic environment team at Bath and North East Somerset Council before the scheme was given the thumbs-up.
Jill Rayson, senior partner at DLG Architects' London office, said: 'The Octagon presented an extremely challenging brief that has commanded great conservation expertise and a significant understanding of effective pedestrian flow to facilitate better use of the site and create new access to hidden areas in the city.'
Work is expected to start on site next month and is due for completion next June.