Diarra made the decision public on Twitter and later confirmed it in an interview with Hearst Connecticut Media.
Diarra, a 6-foot-2 rising junior played 18 games for the Aggies last season, averaging 6.2 points and 1.4 assists.
Diarra's older brother, Mamadou, played for UConn, before injuries forced him to give up basketball. He was a student assistant and later graduate assistant coach for the past three years, receiving a master's degree from the school last weekend. It's not clear if he will return to the program.
Hassan Diarra becomes the third guard to join UConn from the transfer portal, joining Tristen Newton, a transfer from East Carolina, and Nahiem Alleyn, a transfer from Virginia Tech.
The Huskies, who went 23-10 this past season and fell in the first round of the NCAA Tournament to New Mexico State, lost guards, Corey Floyd Jr., Rahsool Diggins, and Jalen Gaffney to the portal, along with forward Akok Akok.
Floyd transferred to Providence; Diggins plans to play next season at UMass; Gaffney ended up at Florida Atlantic and Akok signed with Georgetown.