McGuinness has been a TD since first elected to the Dáil in 1997. He is chair of the Committee on Finance, Public Expenditure and Reform. He entered local politics in 1979 when he won a seat on the Kilkenny Borough Council. He was Mayor of Kilkenny City from 1996 to 1997. He is a former Minister of State and wrote a political memoir entitled: The House Always Wins.