Many of Mann's roles are minor and he frequently delivers only a handful of lines, but he has a somewhat distinctive appearance, that of a long-suffering, vaguely glib demeanor that makes him easily recognizable whenever he shows up in a film or on television. He is, by definition, a character actor, and thus he has never performed a lead role.

His acting career began in the early 1980s, landing guest roles on mainstay sitcoms The Golden Girls and Night Court, and appearances in Who's Harry Crumb? and My Stepmother Is An Alien. His distinctive face and demeanor were featured prominently in 1989's Back to the Future Part II, as the high school student who thinks that Marty has just robbed Biff of his wallet. As Biff regains consciousness after having been knocked out by George, Mann (credited as "CPR Kid," but later labeled by fans as the Wallet Guy) shouts "I think he took your wallet!" after Biff, then turns back to the other onlookers and repeats "I think he took his wallet."

Mann has also appeared in the Hudson Valley Shakespeare Festival in Garrison, New York, for nine seasons.