O'Mahony (spelled "O'Mahoney" during his wrestling career) was brought in to America by a Boston promoter Paul Bowser who had a plan of creating the biggest Irish wrestling star since William Muldoon.

   On June 27th, 1935, O'Mahoney defeated Jim Londos in Boston for the world heavyweight championship, recognized by New York State Athletic Commission and National Wrestling Association. After about a month later, he defeated Ed Don George in Boston to unify the American Wrestling Association title to unify the big three versions of the world heavyweight championships.

   His reign as the undisputed world heavyweight champion ended when Dick Shikat defeated him on March 2nd, 1936 at Madison Square Garden in New York City to become a new champion while O'Mahoney continued to be recognized as the champion by AWA in Boston. However, he lost the AWA title to Yvon Robert four months later.

   O'Mahoney passed away on November 3rd, 1950 in his homeland of Ireland at the young age of 38 due to an injury from an auto accident.