He was first elected to Drogheda Town Council in 1974 as a member of the Labour Party, and was elected to Louth County Council in 1979, serving on the county council until 2003. He contested the 1977 general election as a Labour Party candidate, but was not elected. In 1982, O'Dowd left the Labour Party and joined Fine Gael.[3][4] He served three terms as Chairman of Drogheda Town Council: 1977–78, 1981–82 and 1994–95.
A teacher before entering politics, O'Dowd was elected to Seanad Éireann as a Senator for the Administrative Panel in 1997. He was first elected to Dáil Éireann at the 2002 general election, on his fourth attempt.[5] He was immediately appointed Fine Gael spokesperson for Community, Rural and Gaeltacht Affairs. He was party Spokesperson on Environment, Heritage and Local Government from 2004 to 2007, and on Transport and Marine from 2007 to 2010. In June 2010, he supported Richard Bruton's leadership challenge to Enda Kenny. Following Kenny's victory in a motion of confidence, O'Dowd was appointed as party Spokesperson on Education and Skills.[6]