The Spurs made the announcements Friday and did not disclose terms.
The Spurs also re-signed guard Bryn Forbes on Friday. He appeared in 80 games last season and led the Spurs in 3-point percentage.
Cunningham, a 6-foot-8, 230-pound bruiser, spent last season with New Orleans and Brooklyn, and averaged 5.7 points and 4.1 rebounds in 73 total games. He played the first 51 games for New Orleans, including 24 starts, and averaged 5.0 points and 3.8 rebounds. He was sent to Brooklyn on Feb. 8, and averaged 7.5 points and 4.8 rebounds in 22 games. The nine-year veteran holds career averages of 6.1 points and 3.8 rebounds. His longest tenure was with New Orleans, where he played 263 games.
Belinelli previously spent two seasons with San Antonio and helped the Spurs win the 2014 NBA championship. The 6-foot-5 Italian averaged 10.4 points, 2.7 rebounds and 1.9 assists in 24.0 minutes while shooting .405 from 3-point range in San Antonio.
Belinelli split last season between Atlanta and Philadelphia. In 52 games with the Hawks, he averaged 11.4 points. In 28 regular-season games with the 76ers, he averaged 13.6 points, 1.8 rebounds and 1.6 assists. The 11-year veteran has appeared in 724 NBA regular-season games and holds career averages of 9.9 points, 2.0 rebounds and 1.7 assists. He also has played for Golden State, Toronto, New Orleans, Sacramento, Charlotte and Chicago.
The Associated Press contributed to this report.