The NCAA overturned an earlier decision that made the 6-foot-10 Dieng, who is from Senegal and spent last season at Huntington (W.Va.) Prep, ineligible because of transcript concerns.
Louisville coach Rick Pitino asked the school to appeal the matter, citing Dieng's strong academic record. He began practicing with the team on Tuesday and is expected to play in an exhibition against Northern Kentucky on Sunday.
"I always had confidence and was optimistic that the NCAA would clear him to play," Pitino said. "It restores my faith in that if you do things the right way, things will work out. For the young man and for our program, it's a big boost."
Dieng averaged 15.4 points, 12.6 rebounds and 7.2 blocked shots last season for Huntington Prep. He was ranked 44th nationally by Rivals.com. The Cardinals hope he'll flourish in the wide-open system Pitino plans to use this season.
"When you're running and pressing, having his length back there to alter and block shots is important," Pitino said. "He's a shot blocker, but is also is very skilled offensively. He's got to work himself into our system because he's missed a lot of practice."
Dieng's presence should take some of the pressure off junior center Terrence Jennings, who will replace Samardo Samuels after Samuels left school to head to the NBA following his sophomore season. Dieng's 7-foot-4 wingspan will give the Cardinals an interior defensive presence they've lacked in recent years.
"I can't wait to get in there and block some shots," Dieng said. "I always said I was going to come back. I always said it. I'm just going to focus on listening to coach and playing. That's what is most important for me: just listening to coach and playing."
The ruling is also a rare bit of good news for the Cardinals. Pitino has called this season a "bridge year" and depth will be an issue after the NCAA ruled incoming freshman Justin Coleman and Memphis transfer Roburt Sallie ineligible.
Dieng will likely compete with senior George Goode for a reserve role behind Jennings. The Cardinals open the regular season in their new downtown arena on Nov. 16 against Butler.