Joston began his career as a New York stage actor, and he appeared in many popular television shows during the 1960s, early 1970s, and mid-1980s, but he is best known for his performances in independent films that later achieved cult status, particularly Assault on Precinct 13.

[3][4] After college, Joston moved to New York City and began his professional career as a stage actor in various theater and summer stock productions.

He appeared in a number of popular series including Lassie (in which he had a recurring role), The Virginian, The Rat Patrol, Ironside, The Rookies, and McCloud.

Joston is known for his iconic portrayal of Napoleon Wilson, the sardonic, shotgun-toting, anti-hero in Assault on Precinct 13, John Carpenter's 1976, Howard Hawks-inspired, action film.

Joston's singular performance not only conveys Wilson's stoic toughness, but also emphasizes his irreverent, ironic sense of humor and slowly reveals the character's unexpected capacities for loyalty and tenderness, thereby adding emotional depth and humanity to what otherwise could have been a stereotypical action-hero role.

Moreover, Joston's performance has been repeatedly singled out as the film's best[8][9][10] and is often cited as one of the primary reasons for Assault on Precinct 13's continued audience appeal.

[citation needed] Joston's last film role was in the 1982 B-movie (and Mystery Science Theater 3000 favorite) Time Walker (also known as Being from Another Planet), in which he appeared with his Assault on Precinct 13 co-star, Austin Stoker; and the last two years of his acting career were spent playing guest roles in television series such as Hill Street Blues, Spenser: For Hire, Knight Rider, and Remington Steele.

[3] Some, including director Quentin Tarantino, consider Joston to have been a vastly underrated actor whose talent was not duly recognized during his lifetime.