Walker pitched all or part of six seasons in Major League Baseball (MLB), from 1972 until 1977, for the Montreal Expos, Detroit Tigers, St. Louis Cardinals and California Angels.

After graduating from George D. Chamberlain High School in his native Tampa in 1966,[2] Walker was selected by the Baltimore Orioles in the 1968 January amateur draft.

[1][3] On August 4, 1971, while playing for the Dallas-Fort Worth Spurs in the Double-A Dixie Association, Walker threw a 15-inning no-hitter to beat the Albuquerque Dodgers 1–0.

[4] In 1972, while playing winter ball in Puerto Rico, Walker and several other players helped Roberto Clemente load a plane carrying relief supplies to survivors of the Nicaragua earthquake after Christmas.

A few hours later, Walker returned to his condo and saw the news reports that Clemente's plane had crashed off the coast of Isla Verde, Puerto Rico.