Clavell was the Mountain West Conference player of the year at Colorado State last season. He averaged a league-high 20.4 points with 6.3 rebounds and 1.7 assists in 27 games for the Rams.
The 6-foot-4 Clavell is the second Puerto Rican native with the Mavs, joining guard J.J. Barea. His signing Tuesday came three weeks after Dallas signed 6-11 forward Maxi Kleber, who is from Dirk Nowitzki's hometown in Wurzburg, Germany.
In five games with the Miami Heat's summer league team in Las Vegas, Clavell averaged 12.4 points and 1.4 assists. He shot 41 percent from 3-point range and made 11 of 12 free throws.