The actor, who portrays a young incarnation of the X-Men leader in Matthew Vaughn's prequel, told Comic Book Movie that it was the opportunity to redefine the character that initially drew him to taking on the role.
"With my character, Charles Xavier, he happens to represent for me what is the exact opposite of Charles in the other movies," McAvoy said, referring to Bryan Singer's original X-Men films. "[In the original films] he's quite a saint, he's very sober, he's a proper hero in a lot of ways and he's a real leader of men.
"I saw enough there to make me feel that I could go quite far and have a lot of fun with doing the exact opposite of those things and making him quite irresponsible to begin with, and selfish and have a bit of an ego and definitely having a sex drive as well," the actor continued.
McAvoy admitted that he is hopeful X-Men: First Class will inspire a whole new trilogy of films, as he would like the opportunity to bring his interpretation of Xavier up to date with Patrick Stewart's portrayal of the character.
X-Men: First Class is due out in cinemas on June 3.
Watch James McAvoy in the trailer for X-Men: First Class below: