In his 60-year career, Mercer provided play-by-play broadcasting for several minor league teams: First, the Muskogee Giants of the Class C Western Association, then the Dallas Rangers (Triple A baseball) from 1959–64, and the Dallas-Fort Worth Spurs (Texas League baseball) from 1965 to 1971. He then moved up to broadcast for major league baseball's Texas Rangers (major league baseball) in 1972 (with Don Drysdale) and Chicago White Sox in 1974.