A United States Air Force veteran and attorney, Gardner was elected to the Colorado House of Representatives as a Republican in 2006.

[3] On January 9, 2024, Gardner announced that he was running for United States House of Representatives Colorado 5th Congressional District in the 2024 elections, replacing retiring Congressman Doug Lamborn.

[6] After leaving active duty in 1989 at the rank of lieutenant colonel,[5] Gardner became an attorney in private practice, specializing in government contract law,[7] representing public contractors and charter schools.

[7] From 1993 to 1997, Gardner served as chair of the El Paso County Republican Party[5] and was involved in numerous candidate and issue campaigns in the Colorado Springs area.

[citation needed] In 1999, Gardner was treasurer for the Colorado Springs Safety Association, a group opposing a ballot measure to grant police and fire personnel collective bargaining powers.

[12][13] He played a prominent role in the formation in 2004 of Citizens for Student Achievement and Progress, a local political committee formed to support "education reform candidates and issues" in El Paso County,[14] In 2005, he was a spokesperson for the Colorado branch of All Children Matter, a national political group supporting school choice.

[15] In 2004, Gardner worked on the campaign for a local ballot measure to increase taxes to support The Resource Exchange, a nonprofit serving people with developmental disabilities.

During the campaign, he submitted, for anonymous publication in voter guides, statements opposing the tax increase including: "The families of people with mental retardation, [should] not expect the government to help," and "By funding programs to care for these children, we are encouraging irresponsibility."

[15][23] Gardner was also involved in the contested Republican primary for Colorado's 5th congressional district that year, supporting Jeff Crank over victor Doug Lamborn.

[27] In 2006, Gardner sought the house seat held by retiring Rep. Keith King; he faced no opposition for the Republican nomination.

[28] Gardner won his seat in the Colorado House of Representatives in the 2006 general election, defeating Democrat Anna Lord with about 59% of the popular vote.

[39] Gardner unsuccessfully attempted to add some of his bill's stiffer penalties for striking into the competing measure,[40] which was signed into law by Gov.

[43] Gardner's proposal, which would have directed 2 percent of annual budget increases to services for the developmentally disabled, won the endorsement of an interim legislative committee.

[54] Gardner proposed a state constitutional change that would deny bail to illegal immigrants arrested for some felonies and serious drunk driving offenses.

[60] During the final weeks of the campaign, Lord accused Gardner of conflicts of interest because of his law firm's focus on lobbying, government contracts, and policy formation.