Born in Atlanta, Hearn attended Georgia Tech and signed with the St. Louis Cardinals in 1942.

He spent two years in the minor leagues and three performing military service in the United States Army during World War II, before being called up in 1947.

After compiling a 21–17 record for the Cardinals over all or parts of four seasons, he was placed on waivers and claimed by the New York Giants on July 10, 1950.

He then went on to lead the National League in earned run average (2.49) and win 11 of 14 decisions for manager Leo Durocher that season.

[5] An excellent golfer, he opened a golf school after his baseball career ended.