The pair will star as the same character at different ages in the upcoming sci-fi/action project from Rian Johnson.
The film follows Gordon-Levitt's hitman Joe as he receives an order to kill his future self (Willis).
Emily Blunt, Paul Dano, Noah Segan and Garrett Dillahunt will also star in the film.
Looper opens at cinemas on September 28.
Watch the trailer for Looper below: