Selected by the Atlanta Thrashers with the No. 3 pick in the 2008 NHL Draft, Bogosian made the club out of training camp that year. When he made his NHL debut Oct. 10, 2008, against the Washington Capitals, he became the youngest player in Thrashers history at 18 years and 87 days.
Bogosian broke his left leg Oct. 28, 2008, in a game against the Philadelphia Flyers and was out until January. He scored his first NHL goal Jan. 17, 2009, against Nashville Predators goaltender Pekka Rinne, and led rookie defensemen with nine goals that season. He followed it up by playing for the United States at the World Championship in 2009.