Smithson was born in Stockton-on-Tees in north-east England. While studying architecture at Durham University (1939-1942), he met Alison Gill, whom he later married, in 1949. Together, they joined the architecture department of the London County Council before establishing their own partnership in 1950.
Their style draws heavily on influences from Ludwig Mies van der Rohe, leaning towards minimalism. They were associated Team 10 and its revolt against old Congrès International d'Architecture Moderne (CIAM) philosophies, arguing instead for 'streets in the sky' where inhabitants could live and work, and with the Independent Group (an off-shoot of the Institute of Contemporary Arts}.
Their projects included: