Grenville belonged to a family which had settled in Devon soon after the Conquest. The family property as held in the early 14th century consisted of the manors and advowsons of Kilkhampton and Bideford. These estates, on the border between the counties of Devon and Cornwall, explain how Grenville, who was resident in Cornwall, naturally gravitated to Devon wherein lay the thriving port of Bideford. Through his marriage, which took place before his father-in-law’s death in 1391, he shared the Burghersh estates with Thomas Chaucer, who married his wife’s younger sister, Maud. They included property in Lincolnshire, Oxfordshire, Surrey and Essex, as well as the manor of East Worldham, Hampshire, over which the Burghersh coheirs and their husbands fought a lawsuit with other parties in 1409.
Apart from his more normal activities as justice of the peace and of oyer and terminer, Grenville was concerned on several occasions with special business for the Crown. In 1402 he was a commissioner in both Devon and Cornwall to proclaim Henry IV’s intentions to observe the laws and customs of the realm, and was required to arrest all insurgents. In particular he seems to have had some concern with important military matters. During the Glendower revolt in Wales the King relied heavily on the West Country for men and supplies, and Grenville was ordered in September 1403 to take fish, ale, wheat and other victuals from Devon for consumption by the royal forces at Aberystwyth, Cardigan and Newcastle Emlyn. In the following month, along with the earl of Devon and three other members of the Courtenay family, he was ordered to assemble men and embark from Uphill, Somerset, for the relief of Cardiff. His property at Bideford gave him maritime interests, which had given rise in September 1402 to a royal mandate ‘to put to ransom no Scotsmen lately taken at sea in Devon by him or any of the King’s lieges and now in his custody, until the King shall have full information touching their estates’. Four years later Grenville was still concerned with prisoners: certain men of Devon, captured at sea by Bretons and held to ransom, had sent some of their number back home to raise money. The latter, having reached England, broke parole and, largely for diplomatic reasons, Grenville was ordered to arrest them and send them back.
Grenville’s long career of public service in both Devon and Cornwall, largely on regional business under Richard II and then on affairs of wider import under Henry IV, received some sort of recognition in 1407 when, styled ‘King’s knight’, he was granted the privilege of an exemption from holding office against his will. Even so, he did not refuse a further appointment by the prince of Wales as sheriff of Cornwall, and it was by virtue of this office that he held the parliamentary elections at Launceston on 12 Oct. 1411. He died before the following February. His will, which has not survived, was proved by Bishop Stafford’s commissary, and his heir was his brother, William, who was in possession of Kilkhampton by October 1412. Grenville’s daughter by Margaret Burghersh died before him. Within five years his widow married John Arundell II, eldest son of (Sir) John Arundell I of Lanherne, the steward of the duchy of Cornwall.