O'Brien is the director of the Tunbridge Trilogy, three films that focus on the rural life of Tunbridge, Vermont. The director refers to his style of filmmaking as "community cinema" and his films as "anthropological comedies" as his cast consists mostly of local friends and neighbors from Tunbridge who play themselves in fictional stories. The most famous of these, Man with a Plan, starred the dairy farmer and one time politician, Fred Tuttle. According to O'Brien, the film, in which Tuttle runs successfully for congress, was inspired by 1979's Being There, a movie in which Peter Sellers, a gardener named Chance, becomes a trusted adviser to the presidency. In 2001 it was reported that Man With A Plan had sold 40,000 copies, most of them to Vermonters. O'Brien's other films include Vermont Is for Lovers and Nosey Parker.
In March 2005, O'Brien received the Maverick Award from the Chlotrudis Society for Independent Film for "creating films that Chlotrudis describes as sifting nonfiction and storytelling together in Mike Leigh fashion to create vivid northern New England tableaux.""