The first major role Ethan landed was his comedic performance as Willam Black in Mallrats, directed by Kevin Smith, alongside Jason Lee. Smith recast both Suplee and Lee in later films Chasing Amy, and Dogma. They both make cameos in Clerks II. He went on to a guest starring role as Frankie "The Enforcer" Stechino in Boy Meets World, from 1994-1998. Suplee's notable dramatic performances include the roles of the obese Nazi skinhead Seth in American History X, a Goth in The Butterfly Effect, football player Louie Lastik in Remember the Titans, Johnny Depp's buddy and initial drug-dealing partner Tuna in Blow, and the simpleminded Pangle in Cold Mountain. Suplee also had an uncredited cameo in the HBO TV series Entourage as the scene-mate of movie star Vincent Chase in the fictional movie Queen's Boulevard.
| Year | Title | Role |
|---|---|---|
| 1994 | Boy Meets World (TV) | Frankie Stechino |
| 1995 | Mallrats | Willam Black |
| 1997 | Chasing Amy | Comic Fan |
| 1998 | American History X | Seth Ryan |
| Desert Blue | Cale | |
| 1999 | Tyrone | Joshua Schatzberg |
| Dogma | Noman the Golgothan (voice) | |
| 2000 | Takedown | Dan Brodley |
| Road Trip | Ed | |
| Vulgar | Frankie Fanelli | |
| Remember the Titans | Louie Lastik | |
| 2001 | Don's Plum | Big Bum |
| Blow | Tuna | |
| Evolution | Deke | |
| 2002 | John Q | Max Conlin |
| The First $20 Million Is Always the Hardest | Tiny | |
| 2003 | Cold Mountain | Pangle |
| 2004 | The Butterfly Effect | Thumper |
| Without a Paddle | Elwood | |
| 2005 | Neo Ned | Johnny (orderly) |
| My Name Is Earl (TV series) | Randy Hickey | |
| Entourage (TV series) | Unnamed (cameo appearance) | |
| 2006 | Art School Confidential | Vince |
| The Fountain | Manny | |
| The Year Without a Santa Claus | Jingle | |
| Clerks II | Teen #2 | |
| 2007 | Mr. Woodcock | Nedderman |
| American Pie Presents: Beta House | Fraternity Geek |