St. Cler’s father, probably the most important tenant of the duchy of Lancaster in Sussex, also held substantial estates in four other shires. For the most part these passed on his death in 1387 to his elder son, Sir Philip, who by marrying the Lovein heiress became one of the most prominent landowners in south-east England.
Thomas had followed his brother, Sir Philip, into the circle of local gentry attached to the earls of Arundel, and it was doubtless for this reason that they both purchased royal pardons in 1398, a few months after Earl Richard’s condemnation and execution for treason. Sir Philip’s death in 1408 and the minority of his son, John, then the principal heir to the St. Cler estates, left Thomas as the adult head of the family. However, he could exert no control over his nephew’s landed inheritance, custody of which was sold by the Crown for 1,000 marks to (Sir) John Pelham, the new earl of Arundel’s rival for political hegemony in Sussex. It is quite clear where St. Cler’s loyalties lay; and before long he was in receipt of an annuity of £20 charged on Earl Thomas’s lordship of Lewes. In the autumn of 1409 he was made a prisoner in the Tower, apparently because of a serious dispute involving the earl; and the order issued for his release on 21 Oct. coincided with that for the release of his fellow Fitzalan retainer, Richard Wayville, imprisoned at Nottingham castle. St. Cler doubtless owed his election to Parliament in 1414 to the influence of his lord, then at the height of his power as treasurer of the Exchequer. In May 1415 when the earl was making preparations to go to France on Henry V’s expedition, he named St. Cler among the trustees of his lordships and manors in Sussex and Surrey; furthermore, the force which was mustered under his banner on 1 July prior to embarkation included this retainer among the men-at-arms. It is uncertain whether St. Cler returned home from Harfleur early in October in the company of Arundel, then dying of dysentery, or continued on campaign with the depleted English army to win victory at Agincourt.
St. Cler survived the earl of Arundel by just a year: having made his will on 5 Oct. 1416, he died three days later. He was buried in the parish church at East Grinstead, to which he left £2 for repairs and new paving. Other bequests went to the church at Lingfield, while a priest was to be paid eight marks to pray for his soul. He left three sons, about whom, however, nothing more is heard. His widow later married John Nelond, whom he had named as her fellow executor of his will.
