The actress - who recently welcomed a son with husband Kit Harington - is to appear opposite "Divergent" 's Theo James in the upcoming HBO show, based on the Audrey Niffenegger novel of the same name.
The series, which has been in development since 2018, is described as an "intricate and magical love story that tells the story of Clare (Leslie) and Henry (James), and a marriage with a problem... time travel."
"Doctor Who" writer Steven Moffat is to write and executive producing the show.
The two old pals, who starred together in the "Ocean's Eleven" films and "Money Monster", will play a divorced couple trying to stop their daughter from rushing into marriage in Ol Parker's film.
Parker, who took charge of the "Mamma Mia!" sequel, "Here We Go Again", co-wrote the script with Daniel Pipski.
Clooney and Roberts will also serve as producers of the film, set in Bali.
It will not be the first time Julia Roberts films a movie in Bali.
Back in 2009, the actress flew to the exotic island in Indonesia for Ryan Murphy's "Eat, Pray, Love". Released in 2010, the biographical romantic drama was based on Elizabeth Gilbert's book of the same title.