He was signed by the Boston Braves in 1950, and made the Milwaukee club in 1957 at age 27. His one all-star appearance came in 1958. He also pitched in the ’57 and ’58 World Series for the Braves, finishing 3 games in each series.
In May 1962 McMahon was sold to the expansion Houston Colt .45s. This began a series of short-term stints with a number of clubs. On the final day of the 1963 season, he was sold to the Indians, where he remained until June 2, 1966. On that day he was traded to the Red Sox for reliever Dick Radatz, and on the same date in 1967 moved on to the White Sox for 2nd baseman Jerry Adair. He missed out on Boston’s appearance in the ’67 World Series, but the following July he was traded to the Tigers for pitcher Dennis Ribant, and so was able to play in the 1968 Fall Classic.
In August 1969 Don made his last move – a trade to the Giants. He manned the bullpen there until his release following the 1972 season.
Topps’ 1973 managers cards also feature thumbnails of the coaching staff, and Don was on the Giants’ card as their pitching coach. He was re-activated in late June, and released following the ’73 season. This process repeated itself in 1974, although he gained his final release in early July, just 5 weeks after being reactivated.
He retired at age 44 as the oldest player in the majors. Don pitched for 18 seasons (1957-74) and appeared in 874 games, all but 2 as a reliever. At that time, only Hoyt Wilhelm, Lindy McDaniel, and Cy Young had pitched in more games.
McMahon passed away in July 1987 at age 57.