On July 6, 1961, he was promoted from manager of the Triple-A Portland Beavers to the Cardinals to serve as a Major League coach under new skipper Johnny Keane.

Two months later, on July 13, 1966, Benson returned to the National League as a coach for fellow North Carolinian Dave Bristol, newly appointed pilot of the Cincinnati Reds.

He spent the remainder of his MLB career in the Senior Circuit, as a coach for the Reds (through 1969), the Cardinals again (1970–1975), Atlanta Braves (1976–77), and San Francisco Giants (1980), working in the latter two posts under Bristol once again.

After the club lost 21 of its first 29 games, Dave Bristol was sent on a "scouting trip" on May 10 and replaced by the team's owner, Ted Turner, a world-class yachtsman and television executive who had no baseball experience.

When Turner's appeal to Commissioner Bowie Kuhn was turned down, Benson stepped in for one game—which he won, 6–1 over the Pittsburgh Pirates on May 12—before Bristol was rehired for the remainder of the season.