He studied classical languages, education, and theology at Pennsylvania's Ashmun Collegiate Institute for Colored Youth (renamed Lincoln University in 1866).

[3] Backed by Black civil rights activist and restaurateur George T. Downing, Van Horne ran for the Newport School Committee in 1871 and won his election.

Downing and Van Horne collaborated to help integrate the state's public schools in the aftermath of the American Civil War.

He and Downing championed passage of Rhode Island's Civil Rights Act of 1885, which mandated equal access to public transit, lodging, and dining for all persons regardless of race or previous condition of servitude.

Accused of meddling in local politics and of financial irregularities at the consulate, Van Horne faced charges of incompetence and neglect of duties, impeached, and removed from office on July 31, 1903.

Seventy prominent West Indian merchants and officials petitioned for his reappointment, but President Theodore Roosevelt upheld the impeachment.

The couple had four children: daughters Florence V. (Miller) and Louisa S. A., and sons Mahlon H. and Mathias Alonzo Van Horne.