Hannan played junior hockey in the Western Hockey League (WHL) for the Kelowna Rockets before being selected in the first round, 23rd overall, by the San Jose Sharks in the 1997 NHL Entry Draft. He made his NHL debut during the 1998-1999 season with the Sharks and quickly established himself as a reliable stay-at-home defenseman.
During his time with the Sharks, Hannan became a mainstay on their blue line and was known for his ability to shut down opposing forwards. He was a physical presence and a shot-blocking specialist, often sacrificing his body to protect the net. Hannan's defensive skills earned him a reputation as one of the league's top shutdown defensemen. He was a little rough around the edges at the finesse game, but he was a tenacious, efficient and intelligent defender.
In 2007, Hannan joined the Colorado Avalanche as a free agent. He spent four seasons with the Avalanche, during which he continued to excel defensively and provided leadership on and off the ice. After his tenure in Colorado, he played for the Washington Capitals, Calgary Flames, and San Jose Sharks again before retiring from professional hockey in 2016.
Throughout his NHL career, Hannan appeared in 1,055 regular-season games, scoring 38 goals and recording 123 assists for a total of 161 points. While he was not known for his offensive contributions, his presence on the ice was invaluable for his ability to shut down opposing forwards and contribute to his team's defensive success.
Hannan also represented Canada internationally, winning a gold medal at the 2004 World Cup and a silver medal at the 2005 World Championships.
After retiring, Hannan remained involved in hockey and worked as a development coach for the Oakland Jr. Grizzlies, a youth hockey organization based in Michigan. He also participated in alumni events and charitable initiatives associated with the NHL.
Overall, Scott Hannan's NHL career was defined by his defensive prowess, physicality, and shot-blocking abilities. He was a reliable defenseman who provided stability and leadership to his teams throughout his career.