Although series co-creators Larry David and Jerry Seinfeld wrote the bulk of the show's episodes during the early seasons, Charles was their second in command during this period.

In the season two episode "The Baby Shower" Charles wrote a dream sequence in which the title character, Jerry Seinfeld, was killed.

Charles's episodes also covered such controversial topics as Nazis (in "The Limo"), a psychotic stalker (in "The Opera") and a hospital patient committing suicide (in "The Bris").

A season two episode he wrote, "The Bet", concerning Elaine buying a handgun to protect herself, was never filmed because NBC, some of the cast, and the show's director felt the gun content was too provocative.

[11] Charles's feature debut was Masked and Anonymous (2003) which he directed, and co-wrote with Bob Dylan (under the pseudonyms Rene Fontaine and Sergei Petrov, respectively).

"[12] In an interview, Charles discussed how, because of the nature of the mockumentary process, he had to act as well, even if none of his performance made it to the screen: "We all, especially me, had to play a character as well.

[16][17] In a podcast appearance with Marc Maron on October 5, 2023, Charles described the documentary as the result of a four-hour conversation, adding that he had not spoken to David since the release was canceled.

Charles served as executive producer on two short-lived programs, The Tick (for which he wrote two episodes), and the Dilbert animated series, which he co-developed with Scott Adams and co-wrote the following episodes: In 2000, Charles began his first directorial job on the HBO series Curb Your Enthusiasm, Larry David's follow-up to Seinfeld (which David co-created).