Thompson was also the former mayor of Osgoode Township prior to the amalgamation with the new City of Ottawa.
Prior to being mayor of Osgoode, Thompson was a municipal councillor in the township for 14 years.
In the first municipal elections for the amalgamated city, held in 2000, Thompson won a majority of the vote, defeating John Cyr and Dwayne Acres.
Of all the winning candidates of the 2006 municipal elections, Thompson had the highest percentage of donations coming from corporations (81.9%).
[3] In 2010, Thompson won two thirds of the vote in his ward, defeating Mark Scharfe and Bob Masaro.