Morrisonn started his hockey career with the Vancouver Thunderbird Minor Hockey Association (VTMHA). After proving himself at the community level, he was drafted by the Kamloops Blazers of the WHL and subsequently drafted in the 1st round, 19th overall by the Boston Bruins in the 2001 NHL Entry Draft. He was later dealt to the Capitals on March 3, 2004 in the trade that sent Sergei Gonchar to the Bruins.