When his brother, Thomas, the 12th Earl of Desmond died, Thomas' grandson, James, was in theory Earl, but James was never in de facto possession. Rather John was de facto earl until his death, and then John's son, James, became 14th earl.

Succeeded his grandnephew James 67 years after the death of his father. His great age at his accession to the Earldom induced him to assume the habit of a Dominican friar in the abbey of Tralee, where he died in 1536.30