The film will be a parody of the paparazzi and tabloid interest in 43-year-old Anistion's life, reported Ace Showbiz.
"Theroux is helping Aniston write and direct the project, and they'll shoot it in July," a source said.
Produced by Smartwater, the film is planned to be part of a new viral ad for the brand she endorses.
Aniston and Theroux have been dating for a year.
