Alexander, a junior, told coach Bobby Petrino on Friday about his decision.
Alexander, rated by ESPN's Mel Kiper Jr. as the No. 7 cornerback for the 2018 draft, has struggled through injuries all season. He sprained his knee in the opener and missed the next four games. He aggravated the injury and missed two more games before returning for the final three. His presence made a huge difference for the Louisville defense, which struggled without him.
In six games, Alexander had 19 tackles and one interception.
"I know it was a very difficult decision for Jaire," Petrino said in a statement. "I appreciate the contributions he made to the program over the last three seasons, and I wish him all the best in the future."