Seidenberg played with Adler Mannheim in Germany prior to coming to North America. A sixth-round pick by the Philadelphia Flyers (No. 172) in the 2001 NHL Draft, Seidenberg helped their American Hockey League affiliate, also located in Philadelphia, win the Calder Cup in 2005.
Seidenberg made his NHL debut on Oct. 10, 2002, with the Flyers at the Edmonton Oilers and scored his first NHL goal on Oct. 31, 2002, against the Phoenix Coyotes in Philadelphia. He had 11 points (one goal, 10 assists) in 25 playoff games for the Boston Bruins in 2011, helping them win the Stanley Cup.