Wainwright joined the Liberal Party while studying at Cambridge University and contested Pudsey for the Liberals in 1951 and 1955, then stood three times for Colne Valley before being elected. In 1953 he was elected to the party executive and served as party chairman (1970-72). In the 1950s and 60s Wainwright was one of a group of Liberals who sought to strengthen and professionalise the party. In 1961 he set up and funded the Local Government Department at Liberal HQ and chaired the Liberal Party Research Department (1968-70). In parliament Wainwright spoke for the party on finance, trade and industry and finally employment. 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.