In his debut, on July 6, 1957, against the Boston Red Sox, he failed to retire a batter, issuing bases on balls to Mickey Vernon and Jackie Jensen, then uncorking a wild pitch.

However, he was consistently more effective as the season progressed, and threw a four-hit, complete game shutout against the Washington Senators on September 4, beating Camilo Pascual 1–0 for his first big-league victory.

[4] He went three innings and allowed one run on two hits and one base on balls, and was credited with the win in a 5–3 AL victory at Los Angeles Memorial Coliseum.

Later that season, on September 11, 1959, he hurled a 16-inning, complete game shutout against the eventual league champion Chicago White Sox, winning 1–0.

From 1995 through 2007, Walker was the vice president and director of player personnel in the front office of the St. Louis Cardinals, working as a key assistant to then-GM Walt Jocketty.