He sat in the Legislative Assembly of Ontario from 1999 to 2003, representing the riding of Carleton—Gloucester (renamed as Ottawa—Orléans) for the Progressive Conservative Party.
After sitting as a backbencher for two years, Coburn was appointed to the government of Mike Harris as Minister of Agriculture, Food and Rural Affairs on February 8, 2001.
[2] In 2002, Coburn endorsed Ernie Eves to succeed Mike Harris as leader of the Progressive Conservative Party.
The presence of Quebec workers was no longer an issue, and many local residents were angered by increased energy rates under the Harris and Eves governments.
Despite gaining endorsements from several local newspapers, Coburn lost to Liberal Phil McNeely, another municipal politician, by about 4,500 votes.