Carns founded and currently serves as President and Owner of American Metal Technology, Incorporated, and previously owned Modern Sales, Incorporated, and served as Vice President and President of Modern Handling Systems. His business acumen and engineering background positioned him well for his transition into public service. Carns entered politics in 1990 when he was first elected to the Alabama House of Representatives representing District 48, serving until 2006. During this initial tenure, he held several leadership positions including House Minority Leader and Chairman of the Industrial Development and Economic Growth Committee.

After leaving the House in 2006, Carns was elected to the Jefferson County Commission, where he served as President Pro Tempore from 2006 to 2008. He returned to the Alabama House in 2011 following a special election and has served continuously since then, representing District 48. Throughout his legislative career, Carns has been a champion of conservative causes and economic development initiatives. He co-chaired the 18-member Jefferson County Legislative Delegation, being elected by his peers for multiple terms.

Carns authored and passed landmark legislation during his career, including Alabama's first Voter ID law, which established requirements for photo identification at polling places. He also sponsored welfare reform legislation that significantly changed Alabama's approach to public assistance programs. Additionally, Carns was instrumental in establishing the Alabama Holocaust Commission, demonstrating his commitment to historical education and remembrance. His legislative work has consistently focused on pro-business policies, tax reform, and education issues.

Currently, Carns serves as Chairman of the Commerce and Small Business Committee and Chairman of the Jefferson County Legislation Committee. He also holds memberships on the Children and Senior Advocacy Committee and the Shelby County Legislation Committee. His recent legislative efforts include sponsoring constitutional amendments to protect election integrity and supporting measures to reduce tax burdens on Alabama families.

Carns was married to his wife Judy for over 37 years until her death in January 2020. Judy was a well-known conservative activist and strong supporter of President Donald Trump. The couple had three children- Christa, Jase, and Matt, and were blessed with twelve grandchildren. Carns is an active member and elder at Briarwood Presbyterian Church, where he has served in various leadership capacities. He was elected as a Trump delegate to the Republican National Convention in both 2016 and 2020, demonstrating his continued influence within the Republican Party.