James was born about 1490[a] in Munster, Ireland, second but only surviving son of Maurice FitzGerald and his first wife Ellen Roche.

[4] His mother's family, the Roches also were Old English and descended from Adam de Rupe who had come to Ireland from Wales with Robert FitzStephen.

James married Amy, daughter of Turlough O'Brien,[11][12] a pre-reformation bishop of Killaloe (died 1525 or 1526),[13][14] who had not stayed celibate.

In 1520 his father died and was buried in the Dominican friary of Tralee, which had been founded in 1243 by his ancestor John fitz Thomas FitzGerald, 1st Baron Desmond.

In September 1521 Desmond was defeated at the Battle of Mourne Abbey, south of Mallow, County Cork, by the allied forces of Cormac Laidir MacCarthy, 9th Lord of Muskerry, and Thomas the Bald.

[31] By the Treaty of the More in 1525 Henry VIII ended the war with France and then in 1527 by the treaty of Westminster reversed the alliance, now fighting in the War of the League of Cognac (1526–1530) as an ally of France against Charles V. Desmond reacted by also changing sides and allied himself with Emperor Charles V in 1528[32] and 1529[33] The Emperor sent his chaplain Gonzalo Fernandez to see Desmond at Dingle.