He won the safe Labour seat of Gower at the 1997 general election on the retirement of Gareth Wardell. He was elected with a majority of 13,007 and made a very amusing maiden speech on 4 June 1997, in which he defended the cockle industry in his constituency.
Caton participated in the rebellion of Labour MPs voting against the government decision to invade Iraq in 2003, and was one of the 88 Labour MPs to vote against replacing the Trident Nuclear Missile System, Caton having been a member of the Campaign for Nuclear Disarmament for years. Within Parliament, he has spent a long time on the Welsh AffairsSelect Committee and sits with the Socialist Campaign Group of Labour MPs. Martin Caton retired from Parliament at the 2015 General Election.