Coach Greg McDermott confirmed Harrell's decision, which Harrell announced on Twitter on Wednesday night. Harrell's hometown is Denver, and Pioneers coach Rodney Billups is his cousin.
Harrell started 14 of 30 games as a junior and averaged 7.0 points and 6.3 rebounds. He scored a season-high 18 points in a January win over Seton Hall and had 15 rebounds in a November win over UCLA.
Harrell tweeted he was thankful for the love and support he received from coaches, teammates and fans and that he's excited about returning home and playing for Billups.