The pop superstars are among the big name guest stars to make an appearance in the highly-anticipated third installment of the franchise, which reteams Will Smith and Tommy Lee Jones as secret agents in charge of policing extra-terrestrials.
Gaga and Bieber will play aliens who sit on a surveillance board, alongside kooky filmmaker Tim Burton.
Director Barry Sonnenfeld tells Collider.com: "In this (installment) there are a few people that you'll see up on the surveillance board including Lady Gaga, Tim Burton, who probably knows more about aliens than I do, and let's see who else... Justin Bieber."
They aren't the first superstar singers to appear in the series - Michael Jackson played Agent M in the second film in 2002.
See the trailer below...