Number One Riverside in Rochdale was singled out in the British Council of Offices award recently, which also garlanded the glass four-storey block with a 'best of the best' gong.
Landscape architects from Gillespies blended hard and soft landscape together for the Lancashire borough council's waterfront building.
The landscape design draws on the town's past: its strong linear structure is a creative response to the area's textile heritage.
The riverside gardens were created to offer year-round interest, with planting adding to the ecological value of the river corridor.
The marginal planting also acts as run-off areas for rainwater and flood alleviation from the River Roch in bad storms.
The new civic hall was built to rationalise the authority's estate across 33 different sites into one office block and to help trigger wider regeneration.
Number One Riverside is in the east quarter of Rochdale and forms the first phase of a wider masterplan for the area, which aims to capitalise on the town's number-one natural asset: River Roch.
The project also won a Civic Trust commendation and recognition in the Royal Institute of British Architects' North West Awards earlier this year.