Although Corbet’s father, Sir Robert senior, was the youngest of Sir Roger Corbet of Hadley’s three sons, he had nevertheless inherited the family’s widespread estates, which included Hadley and Hatton in Shropshire, Ebrington and Farmcote in Gloucestershire, Kings Bromley in Staffordshire, Standlake in Oxfordshire, Denchworth and Tubney in Berkshire and Assington in Suffolk.
For all but 12 years of his long life, however, Corbet relied almost entirely on income from estates acquired by marriage. His first wife, Alice Langton, brought him property in Hertfordshire at Hoddesdon, including the manor of Langtons, and in Leicestershire at East Langton, property which after his death was to pass to Alice’s daughter Agnes, widow of Sir Robert Sleyght. (Agnes may well have been Corbet’s step-daughter rather than daughter; certainly his own daughter, Sibyl, contested possession).
Corbet’s career is sometimes difficult to disentangle from his father’s, especially in its earlier stages, but it was undoubtedly the father who, knighted by 1359, saw service abroad under Ralph, earl of Stafford, and served his successor, Earl Hugh, as chamberlain. It was he, too, who was appointed to royal commissions in Gloucestershire between 1359 and 1367 and in Suffolk between 1377 and 1398.
Under Henry IV Corbet was twice made sheriff of Oxfordshire and Berkshire and once of Wiltshire. During his shrievalty of the former bailiwick in 1411 he was required, on pain of 200 marks, to keep the peace towards Sir Peter Bessels (for reasons not known). Corbet continued to be a ‘King’s knight’ under Henry V. Since his father’s death his chief place of residence had been Assington in Suffolk, and he was a frequent guest at the house of another local landowner, Alice, widow of Sir Guy Bryan (son of Lord Bryan). In 1414, however, he spent long periods of time in Shropshire, where, as sheriff, he held the elections to the Parliament summoned to Leicester in April, a Parliament in which (despite the ordinance which prohibited the return of sheriffs) he himself represented Suffolk. It was during this assembly that the attention of the King and council was drawn to the excessive lawlessness and violence endemic in Shropshire and the marches, and when as a result the King’s bench held sessions at Shrewsbury that summer, Corbet, as sheriff, was responsible for arraying juries and obtaining indictments of such alleged miscreants as his namesake, Robert Corbet of Moreton Corbet. Because of his high costs and expenses at Shrewsbury at this time he was awarded £50 9s.7d., and furthermore discharged £40 owing on his account. Corbet again conducted the elections at Shrewsbury in the autumn of 1414, he himself once more being returned for Suffolk.
Corbet did not often act as a feoffee-to-uses, but those whom he did serve in this capacity were mostly men of influence in the government, such as Henry IV’s chamberlain and the steward of Henry V’s household, Sir Thomas Erpingham, or of high rank, such as Edward, earl of March. Indeed, in 1415 he acted for the latter as trustee of estates in 13 counties and the marches of Wales.
Corbet died on 5 July 1417, leaving as heir to the family estates his daughter (probably by his second wife), Sibyl, wife of John Greville of Sezincote, Gloucestershire. After Greville’s death without issue in 1444, they were to pass to the son of Sir Robert’s half-brother, Sir Guy Corbet.