Maurice was the eldest son of Sir John FitzGerald and his wife Honora O'Brien.
FitzGerald fought for James II in the Williamite War in Ireland (1688–1691) alongside his brothers John, Daniel of Ballyruddery, and Thomas of Ardglass.
[2] On 30 June 1703 FitzGerald married Elizabeth, second daughter of David Crosbie (died 1717), of Ardfert Abbey, High Sheriff of County Kerry, by his wife Jane Hamilton, daughter of William Hamilton of Liscloony, County Offaly.
Maurice and Elizabeth had three sons of whom:[4] —and nine daughters, known as the "Nine Geraldines", of whom:[4] Their children were raised as Protestants.
Their daughters married into the Herberts (twice), Merediths (twice), Sandes', Creaghs, Stacks, Hewsons, Collis', Rices and Days.