His father was an electrical design engineer chiefly working on the upgrade of the National Grid and latterly in the North Sea oil industry, whilst his mother was a librarian.

He worked for Sheppard Robson and then Sir Terry Farrell at Farrells, before co-founding Pawson Williams Architects in 1987 with fellow architect Terry Pawson, whom he had known since student days at Kingston.

In 2001 he split from Pawson and established his own independent architectural firm, Keith Williams Architects operating as its founder and director of design.

In 2011, he joined the National Panel of the Civic Trust Awards operating as its chair from 2015 to 2023.

National Life Stories conducted an oral history interview (C467/136) with Keith Williams in 2017-2019 for its Architects' Lives collection.