The actor - who has gained 20lbs since 2009's X-Men Origins: Wolverine - told the Los Angeles Times that director Darren Aronofsky felt that his character needs to put on weight to bring the story to life.
"Darren said with the last one, 'Hey you looked great, but you're so tall that in those long shots you looked kind of like Clint Eastwood, and that's not Wolverine'," he explained.
"He said that Wolverine, in the comics, is powerful, stocky - you know, he's short and thick. So he said, 'I want you to go there, get bigger'."
Jackman added that he believes the project will please fans, saying: "I feel like all the planets are finally aligned to make a great movie.
"I think we're going to make one that people will describe as the best of the bunch."
The Wolverine will hit theatres worldwide in 2012.