He was born near Tunkhannock, Pennsylvanian on January 4, 1823 and passed the bar in 1847, setting up practice in Joliet, Illinois. In 1850 he clerked form the Oregon territorial legislature, moving up to a representative and then speaker of it.

He was a United States district attorney in 1853 and secretary of the Oregon territory 1854 to 1859. After Oregon was admitted to the union, Harding was elected into the state house of representatives from 1858 to 1862. He again served as speaker from 1860 to 1861. He was elected to the United States Senate to fill Edward D. Baker's seat after the latter had died. He served from September 12, 1862, to March 3, 1865, when he retired to his farm near Salem. A few years latter he moved to Cottage Grove, Oregon where he died on June 16, 1899 and was buried.