Inman Horner was born on August 25, 1846, in Philadelphia to Alfred Horner and Elizabeth Driver White.
Horner enrolled in 1861 as a member of the College Class of 1865. He became a member of the Philomathean Society, the University Chess Club, and the Zeta Psi fraternity before leaving at the close of sophomore year.
Horner became a lawyer; he served as vice president of the Philadelphia Law Academy in 1871. He was also a member of the American Philosophical Society and the Numismatic and Antiquarian Society. He died in Philadelphia on November 28, 1912.