Originally from Brisbane in Queensland, he was chosen in the 1999 National AFL Draft at number 37, a trade the Bulldogs had received from Richmond in exchange for Leon Cameron. As at the end of the 2005 season was part of the Bulldogs' leadership group.
The 2006 Record describes Hahn as being "immensely strong" with a "bullocking style of play". During a win against the Brisbane Lions at the Gabba in Round 18 2006, he hyperextended and severely injured his left knee upon landing after a running jump and laid on the ground clutching it. The game was held up as he was taken off on a stretcher. The injury forced him to miss the rest of the season and earlier parts of 2007. He was delisted by the Western Bulldogs on 10 November 2010, but was redrafted only through the Rookie Draft only weeks later.[2] He has a son named Levi.