Key transferred from Alabama in May and will have two seasons left to play in Charlottesville.
Key, a 6-foot-8 forward, will likely slot into Tony Bennett's starting lineup early in the season. Virginia returns Kyle Guy and Ty Jerome in the backcourt and De'Andre Hunter on the wing. With Key, another versatile weapon, Bennett now has four proven options in his rotation.
Key averaged 7.0 points and 5.3 rebounds last season but was hampered by a knee injury that held him out of the first 10 games.
Key earned All-SEC freshman honors in 2016-17 after averaging 12.0 points, 5.7 rebounds and 2.5 assists.
Virginia was ranked No. 5 in the preseason AP poll released Monday. The Cavaliers open the season against Towson on Nov. 6.