In 1976, prompted by his students, Tancredo ran for the Colorado House of Representatives and served two terms in the State Legislature (1977-1981). Tom was a leading voice in opposition to the policies of Democratic Governor Dick Lamm.
Tom was appointed to the Department of Education by President Ronald Reagan in 1981. Tom continued to serve under President George H.W. Bush until 1992. In 1993, Tom became President of the Independence Institute and held the position until 1998.
In 1998, Tom won a tough five-way primary for the 6th Congressional District and then won the general election, becoming only the second person to serve in this position. In Congress, Tom served on the Foreign Affairs Committee and the Natural Resources Committee.
Tom joined the 2008 Republican Presidential Primary. During the campaign, the American Conservative Union ranked Tom ranked #1 of all Presidential Republican candidates with a lifetime rating of 99 out of 100.