Aldo revealed the news Monday night to Brazil-based website Tatame.com.br, and UFC president Dana White confirmed it with ESPN.com on Tuesday.
Pettis, who is next in line for a 155-pound title shot against the Benson Henderson-Gilbert Melendez winner, made his desire to fight Aldo known to White -- via text message -- immediately after watching UFC 156.
It was at that event on Feb. 2 in Las Vegas where Aldo successfully defended his title against former lightweight champion Frankie Edgar by unanimous decision. Pettis sat cageside for the fight.
White responded positively to Pettis' text and a few days later announced that the fight with Aldo was on.
But Saturday night, during the UFC 157 postfight news conference in Anaheim, Calif., White said that Aldo and his handlers did not want to fight Pettis.
"Jose Aldo came out and said, 'There is no way in hell I'm fighting Pettis,'" White said. "He's absolutely refusing to fight Pettis; he doesn't think [Pettis] deserves the shot."
Pettis, the former WEC lightweight champion, has never competed professionally at 145 pounds -- the featherweight limit.
But White said Monday night on Twitter that the fight between Aldo and Pettis is indeed on. The two sides met recently to further discuss the matter and agreed that Aldo would move up to lightweight and challenge for that title should he defeat Pettis.
Aldo is tentatively scheduled to defend his featherweight title against Pettis on Aug. 3. UFC has not yet determined where the fight will take place.
Henderson, the reigning UFC lightweight champ, and Melendez are scheduled to fight April 20 in San Jose, Calif. Melendez is the former Strikeforce lightweight titleholder.