"This was a huge decision for me and my family," Leaf said Thursday. "It was definitely one of the hardest decisions in my life.
"This was the most fun year of basketball I've had in my entire life, and I will definitely miss it. But, I cannot wait to start my new journey."
A 6-foot-10 forward, Leaf averaged 16.3 points and 8.2 rebounds this past season for the Bruins, who made it to the Sweet 16 in the NCAA tournament. He joins Lonzo Ball as freshmen who have announced they will be leaving UCLA.
According to multiple NBA executives, Leaf is expected to be selected in the first round.
"TJ had such a great season for us, and I completely support his decision to pursue his dream," Bruins coach Steve Alford said. "I'm proud of what he was able to accomplish this season. He brought so much to our team, both on and off the court, and we're certainly going to miss him. TJ has been an absolute joy to coach, and I know that all of us at UCLA will be excited to watch him continue to grow at the next level."
UCLA has the No. 2-ranked recruiting class in the nation, including four ESPN 100 top-50 prospects and Ball's younger brother LiAngelo, a three-star prospect.