During his nine NHL seasons he played for the St. Louis Blues, Chicago Blackhawks, Tampa Bay Lightning, and Philadelphia Flyers.

He spent the first ten years of his professional career with both the Blues and their American Hockey League affiliates, the Worcester IceCats and the Peoria Rivermen.

On July 1, 2009, he signed a four-year, $6.8 million deal with the Tampa Bay Lightning.

[2] On July 19, 2010, Walker was traded to the Philadelphia Flyers, along with a 4th-round pick in the 2011 NHL Entry Draft, in exchange for forward Simon Gagné.

[3] Walker's three years in Philadelphia were marred by hip and back injuries, playing in only eight games with the Flyers and 44 games with the Flyers' AHL affiliate, the Adirondack Phantoms.