Riordan first entered politics as an alderman on the
Town of Bowen council. In March 1936, the member for the state seat of
Bowen,
Charles Collins, died and a
by-election was held on the 20 June of that year. Riordan was nominated as the
Labor Party candidate and went on to win the seat over John Smith of the
Country Party. After losing his seat, Riordan found work as a field officer for the State Employment Council and in 1947 he was the
private secretary to his nephew,
Bill Riordan, who was the
Minister for the Navy in the
Second Chifley Ministry. At the
1950 state election, Riordan stood for the reincarnated seat of
Flinders, defeating the Country Party candidate, Mr G. H. Stuart by 297 votes. He held the seat unopposed in 1953, and remained the member until his death the next year. During his time in Parliament, Riordan was Temporary Chairman of Committees on four occasions between 1941 and 1952,
Government Whip from 17 December 1942 until 14 April 1944, and Secretary for Mines and Immigration from 10 March 1952 until his death. ==Personal life==