At the time of the death of Sir Richard Mandeville in x36z the heir to his manor of Astcote was his elder son John, then seven years old; but the latter did not long survive his father and, when Sir Richard’s widow died about eight years later, Thomas was found to be the heir. He became a ward of Roger, Lord Clifford, but in 1375 Edward III granted custody of Astcote to his esquire Robert Corby, an action which prompted Clifford to bring suits against the Crown for loss of his rights of wardship. Mandeville made proof of age in July 1382. Besides Astcote his inheritance included property in Ireland: five years later he obtained royal confirmation of a charter of 1323 whereby Richard de Burgh, earl of Ulster, had conferred on his grandfather Henry Mandeville ‘the attendance of all satellites of the earl’s Bonhaght’ in the province. The charter had been earlier confirmed to Thomas’s father by Lionel of Antwerp.
Naturally, as a member of John of Gaunt’s entourage, Mandeville came into close contact with other Lancastrian retainers. In 1377 he was associated with William Bagot, at that time one of the duke’s esquires, in a discreditable episode involving the abduction of Juliana, widow of Sir Richard Vernon, and her forcible detention at Potterspury and in Warwick castle, although his role in the affair was no doubt that of mere follower to the lead given by the forceful Bagot. Among those of whom he enfeoffed his property in Leicester and elsewhere was William Chiselden, receiver-general of the duke’s estates, and on one occasion (in 1392) he joined the duchy steward of Leicester, Sir Thomas Walsh, in attesting a grant made in mortmain to the borough of Leicester, for which Lancaster’s licence had been required. By Duke John’s grant Mandeville enjoyed an annuity of £6 13s.4d. charged on the duchy lordship of Higham Ferrers. He saw fit to purchase a general pardon from Richard II in June 1398 at a time when Lancaster’s eldest son and heir, Henry of Bolingbroke, was in disgrace, accused of treason; nor can there be any question of where his sympathies lay when Henry was sent into exile. His return to the Parliament of 1399 which deposed King Richard and welcomed Henry’s accession to the throne may be attributed to his long attachment to the house of Lancaster. Subsequently, he was confirmed in his tenure of the area of marshland in Norfolk, now estimated to provide revenues of £8 a year, and on 23 Nov. 1401 as a ‘King’s esquire’ he was awarded a second annuity charged on Higham Ferrers, this one being of 20 marks. He was now given certain tasks in local administration by the Crown, but was evidently reluctant to undertake duties of an arduous nature; he failed to join the royal army which marched into Wales to suppress the rebellion, and in August 1404 he obtained letters patent exempting him from having to discharge any office in future against his wishes.
Mandeville’s marriage to Elizabeth Shulton had given him possession of a moiety of the manor of Countesthorpe and in 1384 he had made settlements regarding this estate as well as the 13 messuages and other property he held in Leicester and its suburbs. Twenty years later Elizabeth inherited from a distant kinsman on her mother’s side the manor of Badger in Shropshire, which, however, she had to share with four female relations. At Michaelmas 1412, after her husband’s death, she and her fellow coheirs to the Shulton lands were faced with lawsuits brought by the Augustinian canons of St. Mary de Pré abbey (Leicester) for patronage of Blaby church and entitlement to an annual pension of £3. She died before 1420, when litigation was still proceeding.