On January 5, 2015, Smith was acquired by the Cleveland Cavaliers in a three-team trade that involved the Knicks and the Oklahoma City Thunder. On April 27, 2015, Smith was suspended for the first two games of the Eastern Conference semifinals after he swung his arm and made contact with the head of Celtics forward Jae Crowder in Game 4 of their first-round series against Boston. In Game 1 of the Eastern Conference finals against the Atlanta Hawks, Smith made eight 3-pointers and scored 28 points in a 97–89 victory. He helped the Cavaliers sweep the Hawks to reach the NBA Finals, where they lost to the Golden State Warriors in six games. During Cleveland's NBA Finals run in the 2015 playoffs, Smith appeared in 18 games (four starts), averaging 12.8 points and 4.7 rebounds in 31.1 minutes per game.