Robert Umfraville's career was predominantly a military one. The chronicler John Hardyng (who entered Umfraville's service sometime between 1402 and 1403) reports that Umfraville fought at the Battle of Otterburn in 1388, as part of the contingent of Henry Hotspur (the son of the Earl of Northumberland). This, says Hardyng, was followed by the first of many border raids Umfraville led into Scotland in 1390. These continued following the deposition of King Richard II, and he probably took part in the Battle of Homildon Hill in 1402. In fact, notwithstanding the regime change of 1399, Umfraville's duties were very much unchanged, and the "old truths remained: royal service, local administration and the defence of the realm." He was indentured to join Henry IV's invasion of Scotland in 1400, which came to very little; Umfraville subsequently inflicted a defeat on a large Scots army at Fulhope Law after an attempted a raid. He continued in defence of the border through the next decade, and his expertise in local politics helped him advise the Warden of the Eastern March, the King's son, John, Duke of Lancaster. Umfraville probably acted in the capacity of 'sub-warden' to the duke, in the now largely defunct middle march. In 1407, with his young nephew Gilbert V de Umfraville, he attended, as a tenant-in-chief, the enthronement of the new Bishop of Durham, Thomas Langley.