Gallinari's deal includes a player option on the second year and will be fully guaranteed, Tellem told ESPN.
Gallinari, joining an improved Celtics bench that will also include guard Malcolm Brogdon, who was acquired in a trade with the Indiana Pacers, will make $17 million-plus this season when adding on to the partial guarantee from his 2022-23 contract before the San Antonio Spurs waived him.
Gallinari, 33, averaged 11.7 points on 38% 3-point shooting for the Hawks last season. In 13 NBA seasons, he has averaged 15.6 points and 4.8 rebounds.
Gallinari has made 1,426 career 3-pointers, the fifth-most by a player 6-foot-10 or taller all-time, according to ESPN Stats & Information research. He trails only Dirk Nowitzki (1,982) Rashard Lewis (1,787) Kevin Durant (1,770) and Peja Stojaković (1,760).