For the next three years, he served as a backbench Member of Provincial Parliament (MPP) supporting the government of David Peterson.
The Liberals lost the 1990 provincial election, though Mahoney was re-elected without difficulty and became Chief Opposition Whip.
Most political observers believed he was attempting to increase his public profile, to be assured of a cabinet position when the Liberals returned to power.
The Progressive Conservative Party won a majority government in the 1995 election and Mahoney was narrowly defeated in Mississauga West by PC candidate Rob Sampson.
After losing the contest, Mahoney told reporters that Parrish was "so low in the gutter that it's a shame that she's standing to represent the Liberal party".
[6] On 17 March 2014, Mahoney announced his candidacy to replace the retiring long-serving Mayor of Mississauga, Hazel McCallion, in the 2014 municipal elections.