Amazon announced Wednesday that it acquired the sci-fi film, which will premiere July 2 on Amazon Prime Video.
Pratt, 41, promoted the movie in an accompanying video.
"It's got aliens. It's got people traveling to the future to fight against aliens. It's got me in it, and it's got aliens!" he said of the film. "Let me just tell you, you ain't ready. This film is so sick."
The Tomorrow War is written by Zach Dean and directed by Chris McKay. The movie takes place in a world where a group of time travelers from the year 2051 return to warn humans about a global war with aliens.
Pratt plays Dan Forester, a high school teacher and father who is recruited to be transported to the future to join the fight. Yvonne Strahovski co-stars as a scientist, while J.K. Simmons portrays Dan's (Pratt) estranged father.
"The Tomorrow War will be a global event that will surprise and delight our customers around the world," Amazon Studios head Jennifer Salke said in a statement. "Director Chris McKay has brilliantly crafted this unique, action-packed sci-fi escape that will keep audiences on the edge of their seats and tug on their heart strings with its father-daughter storyline."
McKay previously directed The Lego Batman Movie. Pratt is known for playing Andy Dwyer on Parks and Recreation and Peter Quill, aka Star-Lord, in the Marvel Cinematic Universe.