Thomas Hartnett graduated from Bishop England High School and attended the College of Charleston. He served in the United States Air Force Reserve and later in the South Carolina Air National Guard. Hartnett currently resides in Mount Pleasant and leads Hartnett Realty, a family-owned real estate firm established in 1947. His son is active in state politics, serving in the South Carolina House of Representatives.

Thomas Hartnett's political identity is rooted in a long-standing family business legacy, with his current role as chairman of Hartnett Realty adding a unique dimension to his public persona. His military service, spanning both the United States Air Force Reserve and the South Carolina Air National Guard, suggests a deep-seated commitment to service and discipline. Notably, Hartnett's legislative alignments reveal an unexpected convergence with opposing factions on environmental regulations, hinting at a highly localized and perhaps regionally protective approach to policymaking. His son's active role in the South Carolina House of Representatives further underscores a familial dedication to public service and influence.