Marvin John Nance (December 21, 1943 – December 30, 1996), known professionally as Jack Nance and occasionally credited as John Nance, was an American stage and screen actor in offbeat or avant-garde film and theatre. He was known for his work with film director David Lynch in a lead role in the film Eraserhead and for his eccentric supporting roles in Blue Velvet and Twin Peaks.

Not to be confused with the Conway Twitty drummer and trumpet player of the same name.

Jack Nance, best known for his role in David Lynch (I)'s TV series "Twin Peaks" (1990), died of possible homicide, Monday 30 December 1996. Nance, a stage actor before working with Lynch in his 1978 cult film Eraserhead (1977), was cast in all of his subsequent films except Elephant Man, The (1980).

Born in Boston of Irish ancestry and raised in Dallas, Jack Nance traveled throughout the country doing children's theater. For eight years he performed with the American Conservatory Theater in San Francisco. Later he became involved with avant-garde theater. He first met David Lynch (I) in the early 1970s in Philadelphia while he was performing in a local theater, and Lynch decided to cast him as the lead in Eraserhead (1977). Originaly it was to be a six-week shooting project, but due to budget restrictions and technical complications, the production and filming took nearly five years to complete. Nance relocated to Los Angeles in the early 1980s, where he appeared in unusual and widely praised films that were not always considered mainstream Hollywood. He has appeared in almost every movie by Lynch, including the TV series "Twin Peaks" (1990), usually playing secondary characters or quirky supporting parts. Nance died suddenly and unexpectedly in December 1996 from an apparent internal head injury the morning after getting into a physical brawl at a donut shop with some rowdy patrons.