Wallace first held political office in 1982 when she was elected to Meath County Council. She served on that authority until 1997. In 1987 she was elected to the 18th Seanad Éireann on the Administrative Panel, having failed to get elected to Dáil Éireann at the 1987 general election. She was successful at the 1989 general election and was elected for the Meath constituency. She retained her seat at each subsequent election, moving to the new Meath East constituency for the 2007 general election.