On 1995 film Mallrats, Mosier worked in organizing the budget along with line producer Laura Greenlee, while presiding over a much larger crew. In the movie, he portrayed Svenning’s assistant, Roddy. The character later appeared on a Jay and Silent Bob MTV short.

On the 1997 romantic comedy film Chasing Amy, Mosier and Smith agreed with Miramax’s Harvey Weinstein and Bob Weinstein to shrink the initial proposed budget from $3 million to $250,000. The compromise allowed Mosier and Kevin to cast their friends instead of established stars. Mosier appears in the beginning of the film as the comics convention patron who gets into an argument with Banky Edwards (Jason Lee) after demeaning his career as a tracer.

On the 1999 film Dogma, Mosier worked with Greenlee again; the editing of the film lasted nearly a year. He also played the Smooching Seaman who Ben Affleck and Matt Damon meet on the bus.

On the 2001 film Jay and Silent Bob Strike Back, Mosier worked with a budget of $20 million. The editing was difficult, due to the MPAA threatening to give the film an NC-17 rating. In the film, Mosier played the assistant director on the set of the fictional sequel to Good Will Hunting and reprises his Willam Black character from Clerks.

Mosier produced Clerks II in 2006. Smith stated he edited the film himself, making Clerks II one of three films Mosier has produced with Smith, but not edited (the others being Mallrats and Zack and Miri Make a Porno). Mosier makes a brief cameo as a concerned father who shields his daughter’s eyes from the sight of a character sitting on a toilet.

Mosier was personally involved with fellow producer Monica Hampton for a while, whom he met while the two were producing Vulgar. He married girlfriend Alex Hilebronner on September 1, 2006. The couple met on the set of Jersey Girl.

In 2007, Salim Baba, a short documentary Mosier produced, was nominated for an Academy Award. Filmmakers Tim Sternberg and Francisco Bello received the nomination (Mosier was unable to be nominated due to a limit of two nominees per short film).

In 2008, Mosier worked again with Smith as the producer on Zack and Miri Make a Porno.

On August 10, 2011, Mosier stated on Twitter that he has written some episodes of the Ultimate Spider-Man cartoon on Disney. This was confirmed in a special “SModcast Extra” (attached to SModcast No. 204 and episode 5 of the Comic Book Men podcast “Secret Stash”) in which he and Smith interview Joe Casey; Mosier has written six scripts for the series.

Mosier served as an executive producer, editor, and actor for Bryan Johnson’s Vulgar, an Askew production. He had also served as a producer (along with Smith) on Drawing Flies, A Better Place, and Clerks: The Animated Series; he served as a co-executive producer on Good Will Hunting and Big Helium Dog. He also appeared in cameos in Drawing Flies as the Crying Diaperman, in A Better Place as Larry, and in Vulgar as Scotty. Although he barely recorded any episodes in 2017, Mosier is also a co-host, along with Smith, of the SModcast podcast hosted by the Smith-owned SModcast.com.

Mosier made his directorial debut with Illumination Entertainment’s animated feature The Grinch, based on the book by Dr. Seuss, and co-directed with Yarrow Cheney. It was released on November 9, 2018.