Chiarelli entered politics in 1987, where he ran as a Liberal candidate in the 1987 provincial election in the riding of Ottawa West.

[5][6][7] Chiarelli endorsed Dalton McGuinty's bid to lead the Ontario Liberal Party in 1996.

The Progressive Conservatives, led by Doug Ford, won a sizeable majority government, ending 15 consecutive years of Liberal power.

[15] The provincial government of Mike Harris did this in 2000, and Chiarelli declared himself a candidate to become the first mayor of the amalgamated city of Ottawa.

[18] In the 2006 election, he ran for re-election against two main opponents: former Kanata councillor Alex Munter, and businessman Larry O'Brien.

Terry Kilrea, runner-up to Chiarelli in 2003, campaigned through the summer but withdrew when it seemed left-wing candidate Alex Munter had taken the lead.

[citation needed] Chiarelli's main project was the expansion of the city's light-rail system: a north-south line would run from Barrhaven to downtown Ottawa starting in 2009.

He introduced a 10-point revitalization plan that would include attracting more jobs and businesses east of the Rideau River in order to improve its economic development.

In a survey conducted by UniMarketing during the week of October 13, 2006, Chiarelli placed second with an 11-point percentage deficit on Munter but had a three-point advantage over O'Brien among the most likely to vote.