The 54-year-old director has helmed the new DC Extended Universe (DCEU) blockbuster and welcomed the opportunity to work on a new movie after directing two Guardians of the Galaxy movies.
James told SFX magazine: "I'd just made the two Guardians movies, I was going to make a third and (this) really came at a time when I needed to be creatively reinvigorated in terms of getting back to what made making movies exciting."
The filmmaker also relished the opportunity to helm a project consisting of supervillains after his work on Guardians.
James said: "If you read the comics, you'll know the DC is no more hard-edged than Marvel, really.
"In some ways when I was growing up, I thought of Marvel as having the harder-edged characters... I think that the difference, for me, between the Guardians movies and The Suicide Squad is that as much as the Guardians are kind of rogues, at the end of the day, we know that they're good."
James also confirmed that not every member of the cast - which includes Margot Robbie, Idris Elba and Sylvester Stallone - will make it to the end credits of the flick.
He said: "People can and do die. It makes the stakes higher and it was one of the reasons why it was really fun for me to deal with these characters, because anything could happen."
Gunn adds that The Suicide Squad' ultimately has similar basic themes to the Guardians of the Galaxy' films.
He said: "This movie is about what every movie I make is about: characters who have a lot of issues and a lot of trauma, trying to find something good within themselves. Some of them fail and some of them succeed.
"There's less sentimentality in this film, but I think there's an equal amount of emotion, if that makes sense."