In 1569, he arrived in Ireland with Sir Warham St. Leger (c. 1525–1597) to arrange for the settlement of lands in the Barony of Kerricurrihy. These had been mortgaged to St Leger by Gerald Fitzgerald, 15th Earl of Desmond. At about this time Grenville also seized lands for colonisation at Tracton, to the west of Cork harbour. Sir Peter Carew had asserted his claim to lands in south Leinster. St Leger settled nearby, and Humphrey Gilbert pushed westward from Idrone along the Blackwater River. All of these English efforts to take over land in the south of Ireland led to bitter disputes. They escalated into the first of the Desmond rebellions, led by James Fitzmaurice Fitzgerald.