A lawyer and hotel owner in the Campbellton area, Van Horne ran for the federal Progressive Conservatives in the riding of Restigouche-Madawaska in a 1955 by-election following the death of Liberal Member of Parliament Joseph Gaspard Boucher.
While in Parliament, Van Horne successfully lobbied the federal and provincial governments to build a bridge between Campbellton and Pointe-à-la-Croix, Québec.
In 1966, after the resignation of Cyril Sherwood, Van Horne successfully ran for leader of the provincial Progressive Conservative Party.
In the 1967 provincial election, Liberal Premier Louis Robichaud was re-elected, and Van Horne resigned as Conservative leader.
In 1975, he left politics entirely after pleading guilty to accepting a bribe over the purchase of park lands and receiving a two-year suspended sentence.