Catcher

He made his major league debut with the Cubs on April 20, 1948, and spent 11 years in the National League as a second-string catcher. He appeared in 608 games played over that span, and his 50 games started as a catcher with the 1950 Cubs were the most of his big-league career. The following season, on June 15, 1951, he was involved in a blockbuster trade with the Brooklyn Dodgers, in which the league-leading Dodgers obtained the Cubs' slugging outfielder, Andy Pafko. But when injury sidelined Brooklyn's Hall of Fame catcher, Roy Campanella, Walker was behind the plate in the deciding game of the 1951 National League tie-breaker series on October 3, 1951, when Bobby Thomson hit the "Shot Heard 'Round the World," costing the Dodgers the pennant.

Walker then backed up Campanella for the next six seasons, the Dodgers' last years in Brooklyn. Over that time, they won four National League titles but Walker appeared in only one World Series, in 1956 against the New York Yankees. He went hitless in two at bats as a pinch hitter. The previous season, Walker was a member of Brooklyn's only world championship team; that year he appeared in 48 regular-season games as Campanella's backup and batted .252.

After retiring as an active player in June 1958, Walker served out the season as a Los Angeles Dodgers' coach. He finished his MLB career with 360 hits, including 69 doubles and 35 home runs. He batted .227 lifetime.

Coach

Walker then was a minor league manager for six seasons. He helmed the unaffiliated Houston Buffs of the American Association for part of 1959, then managed at Double-A in the Dodgers' and Yankees' farm systems from 1960 through 1964. After 1965 he was a pitching coach for the Washington Senators, New York Mets and Atlanta Braves, working closely with managers Gil Hodges, Yogi Berra and Joe Torre, among others. Walker was the Mets' pitching coach for 14 seasons, from 1968 through 1981, including service on the 1969 World Champion "Amazin'" Mets. He also served as the club's emergency manager from September 25–29, 1968, after Hodges suffered a mild heart attack and went on medical leave for the final four games of the season; under Walker, the Mets were 2–2. As the Mets' pitching coach, he supervised Hall of Famers Tom Seaver and Nolan Ryan. Walker scouted for the Braves and St. Louis Cardinals after his coaching career ended.