Rodgers first entered the British House of Commons in 1962, and served in Labour Governments under Harold Wilson and James Callaghan, becoming Secretary of State for Transport in Callaghan's Cabinet in 1976. He held the post until Labour's defeat in the 1979 general election. With Labour drifting to the left, Rodgers joined Shirley Williams, Roy Jenkins and David Owen in forming the Social Democratic Party in 1981.
At the 1983 general election the SDP-Liberal Alliance won many votes but few seats, and Rodgers lost his seat of Stockton-on-Tees. He remained outside Parliament until his appointment to the Lords in 1992. During that time he was Director-General of the Royal Institute of British Architects and also became Chairman of the Advertising Standards Agency.
In 1987 Rodgers was chairman of the successful "Yes to Unity" campaign within the SDP in favour of merger with the Liberal Party. He became the Liberal Democrats' Lords spokesman on Home Affairs in 1994 and was its leader in the Lords between 1997 and 2001. His autobiography was titled Fourth Among Equals, reflecting his position as the least prominent of the SDP's founders.