The sci-fi film, which also stars Bruce Willis and Emily Blunt, sees Gordon-Levitt as a killer who discovers that one of his targets is his future self.
Talking to MTV News, the Dark Knight Rises star had high praise for Looper writer and director Rian Johnson, with whom he previously worked on Brick.
"Looper is, to be honest, some of the best work I've ever done as an actor. I really transformed myself. Rian Johnson, who wrote and directed Brick is - I think - one of the greatest filmmakers going," he said.
"[Johnson] actually has a lot in common with Chris Nolan and Steven Spielberg. He's a brilliant, brilliant guy. I cannot wait for people to see that movie."
Gordon-Levitt went on to add that the recently-released Looper trailer doesn't capture the full scope of the film, explaining: "When you actually see the movie and you really get a sense of what those prosthetics look like, I'm really excited for people to see this character because it's just nothing like me.
"That's my favourite thing as an actor, to create a character that's other than myself."
Watch Emily Blunt discuss Looper below: