Born in Frankfort, Kentucky, the son of Martin D. Hardin, Hardin pursued classical studies and was graduated from Transylvania University, Lexington, Kentucky, where he studied law. He was admitted to the bar in Kentucky in 1831 and commenced practice in Jacksonville, Illinois. He served in the Illinois Militia during the Black Hawk War 1831–1832. He was brigadier general in command during the Illinois Mormon War in Hancock County, Illinois in 1844. He later attained the rank of Major General. He was appointed prosecuting attorney of Morgan County in 1832. He served as member of the Illinois House of Representatives 1836–1842. His son Martin Davis Hardin was born in 1837, and his daughter Ellen Hardin Walworth was born in 1832.