Robert may have belonged to the same family as George Castell, although he is not known to have ever held the latter’s manor at Withybrook. His own landed holdings were all elsewhere in Warwickshire: at some unknown date between 1401 and 1407 he acquired (possibly through marriage) a manor in Luddington (in Stratford-upon-Avon) and a moiety of that of Alspath, and in later years he purchased property at Solihull.
But before he established himself as a landowner Castell had furthered himself through service to Henry IV and, more important, to the latter’s son Henry of Monmouth. As early in the reign as 13 Nov. 1399 he had been described as a ‘King’s servant’ when made a grant of £5, and before a year had passed he had joined the household of the prince of Wales as one of his esquires. In 1401 the prince awarded him for life the offices of clerk and keeper of the mills and fishery of the Dee, permitting him to perform his duties by deputy, and over the next few years he, as a trusted member of Henry’s retinue, was often employed in collecting large sums of money at the Exchequer for the prince’s use. These sums (for example, some £4,000 in 1403) were destined to finance the royal army in the Welsh marches. It is quite likely that Castell took part in the battle of Shrewsbury, and in July 1404 he saw further action in the contingent sent by Prince Henry to Brecon, although later that year he was with the prince’s household when it stayed at Hereford and Leominster.
The accession of Monmouth as Henry V saw Castell installed as a minor official in the royal household. He was returned to Henry’s second Parliament, which met at Leicester in April 1414, there also acting as proxy for the prior of Coventry. Early in 1415 he was involved in organizing the carriage of furnishings for a chamber newly built at Kenilworth; and by that spring he was clerk of the marshalsea of the Household, as such being retained for service on campaign in France. Castell remained in the King’s retinue throughout the expedition, being avener of the Household at the time of the fall of Harfleur and going on in the royal train to meet the French at Agincourt. He evidently distinguished himself in battle, for after his return to England the annuity of £10 which he had been receiving from the issues of Nantwich was increased to £21. Castell is not known to have fought overseas again; and in the last years of Henry’s reign he was active at home as a j.p. and escheator. In February 1418, when he was granted the wardship and marriage of Alan Strange’s heir, such important figures as John Merbury (chamberlain and receiver of South Wales) and John Wilcotes (receiver-general of the duchy of Cornwall) acted as his mainpernors.
Castell’s return to Henry VI’s first Parliament may have placed him in the position of a representative of the minor officials of the household of the late King, who on his deathbed had remitted to them all debts and arrears of account. It was not until the Parliament of 1427, however, that 30 of them, including Castell, successfully obtained formal acquittance and received pardons. Meanwhile, in the early months of the reign, Castell’s offices on the Dee and at Cheylesmore, as well as his £40 annuity, had been confirmed. He now devoted his time to personal affairs: in 1428 he and his wife were engaged in property transactions at Berkswell, near Alspath, and in 1434 he gave up his remaining post, the stewardship of Cheylesmore.
On 5 Mar. 1436 Castell and his wife were involved in an affray at Berkswell caused by their attempts to evict a tenant. He may have been wounded, for he died less than three weeks later, on the 22nd. Not long afterwards his widow married John Folkesworth.