Born in Richmond, BC, Scott Hannan starred with the Surrey Wolves of the BCAHA before joining the Tacoma/Kelowna Rockets of the WHL. The talented rearguard was chosen 23rd overall by the Sharks after he scored 17 goals for Kelowna in 1996-97. He spent two more years in junior and received a five-game look with the Sharks in 1998-99 before splitting the 1999-00 season between the NHL and the AHL's Kentucky Thoroughblades.
A gritty defenceman, Hannan elevated his play in all areas of the game and became a regular on the San Jose defence corps in 2000-01 after splitting the previous year with the Sharks and their AHL affiliate in Kentucky . In his first full season with the club, Hannan averaged over 19 minutes in 75 games and over the course of the next four seasons continued to elevate his game and in 2003-04, became one of the premier young defenceman in the league.
After helping the Sharks reach the Western Conference Final, only to fall short against the Calgary Flames, Hannan was added to Canada's 2004 World Cup of Hockey entry, after defenceman Rob Blake and Chris Pronger went down to injury. Upon his arrival with Team Canada, Hannan, was a key player on a blueline rittled with injuries and went on to help Canada capture its first ever World Cup title.
In the spring of 2005, Hannan helped Canada capture a silver medal at the World Championship. Following a pair of steady seasons with the Sharks in which he competed in his 500th game played, Hannan signed as a free agent with the Colorado Avalanche in the summer of 2007.
On November 30, 2010, Hannan was sent from a young and developing Avalanche team to a Stanley Cup contender in the Washington Capitals in exchange for forward Tomas Fleischmann. He would finish the season with the Capitals and sign as a unrestricted free agent the following summer with the Calgary Flames.
In 78 games for the Flames during the 2011-12 season, the defensive specialist scored twice and added ten assists.
In the summer of 2012, once again a free agent, Hannan signed with the Nashville Predators. He would suit up in 29 games for the Predators during the lockout-shortened 2012-13 season before being traded to the San Jose Sharks in exchange for a draft pick.