Terms of each contract were not disclosed, but Donovan will be paid $826,875 next season, according to CapGeek.com. The 24-year-old had two goals and 14 assists in 52 games for the Islanders in 2013-14. He had seven goals and 14 assists in 27 games for the Bridgeport Sound Tigers of the American Hockey League.
Donovan was New York's fourth-round pick (No. 96) at the 2008 NHL Draft.
Gallant, 25, had no points and 17 penalty minutes in four games with the Islanders last season and one goal, one assist and 255 penalty minutes in 58 AHL games.