He was the eldest son of Thomas FitzMaurice FitzGerald and Rohesia de St. Michel. He is noticed in 1291 in serious dispute with William Vescy, Lord of Kildare, Lord Justice of Ireland, about whom there were many complaints of oppression and neglect of the country's defences. As champion of the complainants John Fitzgerald, by then 4th Lord of Offaly, their paths crossed and instead of addressing the issues Vescy charged Fitzgerald with minor charges of slander and libel. Fitzgerald appealed to King Edward I of England, who, to examine and judge the matter impartially, summoned them both to London to hear the cases, where it appears FitzGerald had the advantage, challenging the Lord Justice to clear his name by combat, which was accepted. However, Vescy fled to France, whereupon the King pronounced Lord Offaly innocent, and settled upon him Vescy's lordships and manors of Kildare, Rathangan, &c., had been forfeited to the Crown. In 1296 and 1299 he was summoned to fight for the Crown in the Scottish campaigns of Edward II. With John Wogan, Lord Justice, and others he went a third time to war in Scotland in 1301-2. In 1307, with his son-in-law Sir Edmund Butler, he dispersed rebels in Offaly who had razed the castle of Geashill and burnt the town of Leix. In 1312 he was sent as General at the head of an army into Munster to suppress armed Irish rebels. On 25 May 1315, Edward Bruce, brother to King Robert the Bruce of Scotland, entered the north of Ireland with 6000 men, was crowned King of Ireland at Dundalk, and wasted the country. Lord Offaly, among others, commenced vigorous sporadic warfare to resist Bruce, leaving "great slaughter" of Scots and the Irish irregulars in his service. Edward Bruce was eventually defeated and killed in the battle of Dundalk. King Edward II created Fitzgerald Earl of Kildare by Letters Patent dated 14 May 1316, the year in which he founded the Augustinian priory at Adare, County Limerick. He died that same year, on Sunday 12 September 1316, at Laraghbryan, near Maynooth and was interred in the Franciscan Friary of Clan. Kildare.
Family
He had married Blanche de La Roche, daughter of John de La Roche, Lord Fermoy and Maud Waley, by whom he had two sons and two daughters:
