From his first 23 pro fights he won 19, drew one and lost three, one of these to Belgian heavyweight champion Lion Ven.
In June 1966 he faced his namesake John McCormack in an eliminator for the British light heavyweight title at the Royal Albert Hall, winning on points.
McCormack made a second defence of his British title against Avoth in January 1969, and lost after being forced to retire in the eleventh round due to a cut to his left eyelid.
In April 1970 he had his final fight, another shot at the British title against Avoth; McCormack was disqualified in the eighth round.
McCormick went on to work with his brother Pat with young boxers at St. Saviours Olympic Boxing Academy on Dorset Street in Dublin.