As a youth, Reasoner played in the 1990 and 1991 Quebec International Pee-Wee Hockey Tournaments with a minor ice hockey team from Rochester, New York. Reasoner was selected in the first round of the 1996 NHL Entry Draft, 14th overall, by the St. Louis Blues. This followed two years of high school hockey at McQuaid Jesuit High School, two years of high school at Deerfield Academy in Massachusetts and three years at Boston College, where he was named Rookie of the Year his freshmen year, and named All-American his junior season when he led the Eagles ice hockey team to the NCAA finals. He skated alongside BC legends Andy Powers and Brian Gionta. Reasoner split 1998–2001 between the Blues and their top minor league affiliate, the Worcester IceCats of the American Hockey League. In 2003, he was voted a starter on the IceCats' tenth-anniversary All-Time Team. On July 1, 2001, Reasoner was traded to the Edmonton Oilers in exchange for Oilers' captain Doug Weight and Michel Riesen. In November 2003, Reasoner suffered a severe knee injury when he crashed into the end boards. During the 2004–05 NHL lockout, Reasoner played 11 games for EC Red Bull Salzburg of the Austrian League. On August 9, 2005, Reasoner signed a one-year contract extension with the Oilers. On March 9, 2006, Reasoner was traded to the Boston Bruins in exchange for Sergei Samsonov. On July 4, 2006, as a free agent, Reasoner signed a two-year contract to return to the Edmonton Oilers. After the expiry of his deal, on July 17, 2008, Reasoner signed a contract with the Atlanta Thrashers. On June 24, 2010, Reasoner and second-round picks in the 2010 NHL Entry Draft ) was traded to the Chicago Blackhawks in exchange for Dustin Byfuglien, Ben Eager, Brent Sopel and Akim Aliu. One month later, on July 22, 2010, due to salary cap restrictions within the Blackhawks' organization, Reasoner was traded to the Florida Panthers in exchange for center Jeff Taffe. After the Panthers traded away captain Bryan McCabe, Reasoner was named an assistant captain. On July 1, 2011, Reasoner signed a two-year contract with the New York Islanders.
