On December 19, 1903 Jack Munroe made his name known and his presence felt in the boxing world by defeating James Jeffries, the World Heavyweight Champion. This bout, a four-round exhibition fight, was held in Montana. Munroe held his own for the first three rounds and knocked Jeffries down for a nine-count in the fourth.

The rivalry continued in San Francisco in 1904, with Jeffries taking his revenge by knocking out Munroe in the second round. Later that same year, Munroe knocked out Peter Maner, the Irish Heavyweight Champion, and Al Limerack of Boston. Munroe and Jeffries met in the ring again in San Francisco in 1904. Jeffries weighed in at 219 pounds and Munroe at 196 pounds. Once again, Jeffries knocked Munroe out in the second round to hold onto his World Heavyweight Title. Munroe was not discouraged and continued his boxing career, knocking out Hank Pardello in five rounds in Savannah, Georgia.

He ended his career on a winning note, his last recorded fight being a six-round win over Alf Allen in Ottawa. Jack Munroe is an Original member of the Nova Scotia Sport Hall of Fame.