Raised in the Greater Vancouver area of British Columbia, Walker spent his youth playing street hockey with consuming NHL goaltender aspirations. That dream never materialized; however, the Expos saw his baseball potential and signed him in 1984. By 1990, Walker became their starting right fielder, propelling them to the majors' best record in 1994 when that year's strike stopped their first serious World Series run. He signed with the Rockies as a free agent following the season, and, during a six-year period starting in 1997, was the major league batting leader three times while finishing second in the NL twice. In 1997, he also led the league in home runs, OBP, and SLG, while joining the 30–30 club, registering 12 outfield assists and leading his position with four double plays turned; he won the NL MVP Award that year. Desiring a trade to a contending team, Walker was sent by the Rockies to St. Louis in the middle of their 105-win season of 2004 where he made his first World Series appearance while tying or setting three Cardinals postseason records. He announced his retirement from playing baseball after Game 6 of the 2005 National League Championship Series.