[1] Some of his best-known acting roles include the title character of the 1960s animated Jonny Quest TV series, Eric "Otter" Stratton in the 1978 comedy film National Lampoon's Animal House, and the recurring role of Vice President John Hoynes in the 2000s NBC drama The West Wing, which earned him two Primetime Emmy Award nominations for Outstanding Guest Actor in a Drama Series.

[3] At age 13, Matheson appeared as Roddy Miller in Robert Young's CBS nostalgia comedy series Window on Main Street during the 1961–1962 television season.

[7] He played the role of the oldest son, Mike Beardsley, in the film Yours, Mine and Ours (1968), which starred Lucille Ball and Henry Fonda.

In 1969, Matheson joined the cast of NBC's television Western The Virginian in the eighth season as Jim Horn.

In the final season of the television Western Bonanza in 1972–1973, Matheson played Griff King, a parolee who tries to reform his life as a worker at the Ponderosa Ranch under Ben Cartwright's tutelage.

In 1980 he auditioned for the role of Indiana Jones in Raiders of the Lost Ark, for which Harrison Ford won the part.

In 1989, he starred in the short-lived sitcom "Just in Time" produced by Warner Bros.[8] Along with business partner Daniel Grodnik, he bought National Lampoon in 1989,[9][10][11] selling it in 1991.

[14][15] He has directed episodes of Third Watch, Ed, The Twilight Zone, Cold Case, Without a Trace, The West Wing, Psych, The Good Guys, Shark, White Collar, Criminal Minds, Suits and Burn Notice (on which he also performed in a recurring role).