Films:
* The Last Picture Show (1971): His film debut as the shy, sensitive Duane Jackson.
* The Groove Tube (1974): A cult classic comedy where Mull plays a variety of roles, including a flamboyant game show host.
* The Big Bus (1976): A goofy disaster comedy featuring a cast of stars, including Mull as a bus driver.
* Clue (1985): Played the role of the "Mr. Green" suspect.
* Risky Business (1983): Played a businessman, Mr. Jones, who hires Joel Goodsen for a "business proposition".
* The Santa Clause (1994): Played the role of Neil Miller, a Christmas-loving toy company executive.
* The Wedding Singer (1998): Played the role of Glenn, a lovable wedding singer.
* Waiting for Guffman (1996): Played Corky St. Clair, a struggling actor.
* A Mighty Wind (2003): Mull starred as the lead singer of the folk trio "Mitch & Mickey".
* Best in Show (2000): Played a dog show judge, a character who is a favorite among fans.
* The Grand Budapest Hotel (2014): Played the role of M. Ivan, a hotel manager.
Television:
* Fernwood 2 Night (1977-1978): Co-created and starred as Marty, a local newsman.
* The Associates (1979-1981): Played Jack, a lawyer.
* The Newhart Show (1982-1990): Recurring role as Michael Harris, a quirky and lovable character.
* Roseanne (1993-1997): Played Leon Carp, the love interest of Roseanne's mother.
* Arrested Development (2003-2006, 2013, 2018, 2019): Played Tobias Funke, a struggling actor and a key character in the sitcom.
* Gary Unmarried (2008-2010): Played Gary's father, a lovable but eccentric character.
* The Middle (2009-2018): Recurring role as Brick's teacher and later principal, Mr. Ehlert.
* The Millers (2013-2015): Played the father of the family.
* Veep (2012-2019): Recurring role as Senator Tom James, a politically ambitious character.
* The Kominsky Method (2018-2021): Played Martin, an agent of the title character.
* Brooklyn Nine-Nine (2013-2021): Recurring role as Nikolaj, Jake's father.
* The Afterparty (2022-present): Played Danner, a detective investigating a murder.
This is just a selection of his impressive career. Mull is known for his dry wit, his impeccable comedic timing, and his ability to portray a wide range of characters.