Wainwright joined the Liberals when at Cambridge University in the late 1930s and stood as Liberal candidate for Pudsley in 1950 and 1951 and then for Colne Valley where he stood three times before being elected in 1966. He was defeated in 1970 but re-captured the seat in February 1974 and held the seat until he retired in 1987. In parliament Wainwright spoke for the party on finance, trade and industry and finally employment. For the party he chaired the party’s research department (1968-70) and served as party chairman (1970-72). On his retirement from parliament Wainwright was actively involved in the Electoral Reform Society and was a founder member of Charter 88. His son Martin has been Northern Editor of the Guardian and his daughter, Hilary is a radical academic and co-editor of Red Pepper magazine.