Sir Gerald Aylmer (ca. 1500–1559) was a judge in Ireland in the time of Henry VIII and played a key part in enforcing the Dissolution of the Monasteries. His numerous descendants included the Barons Aylmer.
He was the younger son of Bartholomew Aylmer of Lyons, Ardclough, County Kildare, and his wife Margaret Cheevers. He married Alison, daughter of Gerald Fitzgerald of Alloone ( a cousin of the Knight of Kerry), and his wife Isabel Delafield, the heiress of Culduffe. His sister Anne married Sir Thomas Luttrell, Chief Justice of the Irish Common Pleas.
In early life he was loyal to Gerald FitzGerald, 9th Earl of Kildare when he served as sheriff of Limerick in the earlier 1520s. As a partisan of Kildare, (the so-called Geraldines) he was made second justice of the Court of Common Pleas (Ireland) on 19 December 1528. He was confirmed in that role on 23 August 1532, then presented a critique of the Geraldine administration at the English court in 1533, along with John Alan. Just before the rebellion of Silken Thomas, Aylmer was appointed Chief Baron of the Irish Exchequer on 25 June 1534. When Sir Bartholomew Dillon died unexpectedly after only one year on the bench, Aylmer was named Lord Chief Justice of Ireland on 12 August 1535.
Aylmer became a principal agent of Thomas Cromwell in Ireland and worked closely with John Alan, Master of the Rolls in Ireland, in bringing about the defeat of Silken Thomas. He assisted various English lord deputies in Ireland in expeditions against the O'Connors (1537) and the Kavanaghs (1538) and was employed in military campaigns against the Geraldines and the O'Neills. He was knighted in the field after the battle of Bellahoe in 1539, and given a grant of the lands of Dollardstown, near Athy, County Kildare