Matthews is not planning to hire an agent, meaning he can return to Ann Arbor next season.
"After careful consideration with my parents and coaching staff, I am excited to announce that I will be declaring for the 2018 NBA draft without hiring an agent," Matthews said on Twitter. "I give thanks to the Lord for this amazing opportunity, as well as the entire University of Michigan for their support. Go Blue!"
Matthews, who was a top-50 recruit coming out of high school, transferred from Kentucky after his freshman season. He sat out the 2016-17 campaign but helped lead Michigan to the national championship game this past season.
Matthews averaged 13.0 points and 5.5 rebounds, but he put up 16.6 points in the first five games of the NCAA tournament before struggling en route to six points in the title game against Villanova.
ESPN's Jonathan Givony projects Matthews, a 6-foot-6 wing, as a first-round pick in the 2019 NBA draft.