Throughout his career, Walker has played right field for the Expos, the Rockies, and Cardinals. During his career, which lasted from 1989-2005, he was named an All Star five times, won seven Gold Gloves, won three Silver Slugger Awards, won the NL batting title three times, was named the 1997 NL MVP, and was the 1997 NL home run champion. 

After the 2005 season, Walker announced his retirement from baseball. In 2009, he was inducted into the Canadian Baseball Hall of Fame.