Born in Stockton, Smithson met his wife Alison (1928-93) when both were studying at the Durham School of Architecture (1939-42). They set up an architectural partnership in London in 1950 and became the most influential members of the British architectural avant-garde.
Their school at Hunstanton, Norfolk (1950-4) in the steel and glass idiom of Mies Van Der Rohe was the first Brutalist building in Britain. The intellectual approach of the Smithsons was exemplified by the fact that they never even visited the building site. Their Economist Building in London (1960-4) is now Grade 1 listed.

Though the Smithsons built relatively little, and some of their work was grim and flawed, they remained hugely influential. Even the failure of their 'streets in the sky' ideas, based on their attachment to working-class street architecture, did not affect their status.