Cleveland made the announcement on Wednesday, a holiday treat for the team's fans still grappling with their emotions after superstar LeBron James announced he's leaving the Cavs for the second time to sign with the Los Angeles Lakers.
The Cavs selected Sexton with the No. 8 overall pick in last month's NBA draft. He averaged 19.2 points as a freshman at Alabama and played his best in big games while leading the Crimson Tide to its first NCAA tournament appearance since 2012.
Now that he's under contract, the 19-year-old can't be traded for 30 days. However, the Cavs are likely to hang on to Sexton and help them rebuild without James, who led Cleveland to four straight NBA Finals and a championship in 2016.
Sexton is on Cleveland's summer league roster for games in Las Vegas.