Guinevere Turner and I Shot Andy Warhol director Mary Harron wrote the screenplay which ended up being selected for the film version of Bret Easton Ellis' American Psycho. She has a brief cameo in the film, in which she delivers the in-joke, "I'm not a lesbian!". (Turner has publicly acknowledged her lesbianism.).

Turner emerged on the scene with the film Go Fish, which she co-wrote and co-produced with her then-girlfriend, Rose Troche. Turner also starred in the film, portraying a young woman named Max whose friends help her find a new girlfriend, Ely, portrayed by VS Brodie. Director Kevin Smith was a fan of the movie, particularly a scene in it wherein, in an imagined sequence, some of a character's friends chastise her for "selling out" and sleeping with a man, and used it as an inspiration for his own take on a similar theme in his own film Chasing Amy. Turner has cameos in both Chasing Amy and Smith's later film Dogma; her name is used as that of Joey Lauren Adams' character in Smith's Mallrats.

A writer and story editor for the first two seasons of The L Word, Turner also made several memorable guest appearances on the show as Alice Pieszecki's screenwriter ex-girlfriend, Gabby. In 2005 Turner wrote the script for BloodRayne directed by Uwe Boll, and the script for The Notorious Bettie Page, with Mary Harron, who directed it. Turner's first foray into web television is the 2008 online drama series, FEED, directed by Mel Robertston, launched on AfterEllen.com.

Turner has directed several short films, such as The Hummer and Hung, which have appeared in many international film festivals.