A resident of West Windsor, New Jersey and attending law school, Hartmann ran for the New Jersey General Assembly in 1991 for the 15th legislative district. In the 1991 general election for the Assembly, incumbent assemblyman Gerard Naples lost his seat coming in fourth place behind fellow incumbent Democrat John S. Watson and Hartmann. Hartmann's running mate took third place, leaving Hartmann and Watson as the winning candidates. Hartmann won along fellow Republican Dick LaRossa, who would serve in the New Jersey Senate. Elected at age 24, this made Hartmann the youngest Republican elected to the Assembly in state history. Hartmann would serve one term in the Assembly before being succeeded by Joseph Yuhas in 1994.[3]
^Manual of the Legislature of New Jersey, Volume 205, Part 2, p. 245. J. A. Fitzgerald., 1993. Accessed March 14, 2023. "John W. Hartmann, Rep., West Windsor - He was graduated from Princeton Day School and, in 1989, received a bachelor of arts degree in history at Georgetown University."