Donovan was drafted 96th overall in the fourth round of the National Hockey League's (NHL) 2008 draft by the New York Islanders. Upon completing his sophomore season at the University of Denver, he was quickly signed to a professional contract by the Islanders, who assigned him to play for their American Hockey League (AHL) affiliate, the Bridgeport Sound Tigers. Donovan scored a goal and four assists during the final six games of 2010–11 AHL season. For the 2012–13 season, Donovan tied Justin Schultz for the most points among AHL defensemen with 48.