The Tirwhits owed much of their importance in Lincolnshire to the successful career of Robert Tirwhit, the distinguished lawyer, who became a King’s serjeant in 1399 and a j.KB nine years later, being also then retained as a councillor for the duchy of Lancaster. That he was in a position greatly to advance his own son’s interests seems certain, for at the time of the latter’s first return to Parliament in 1416, he was active on the bench in both Kesteven and Lindsey (as well as elsewhere) and thus probably played no small part in influencing the electors.
Shortly after his return from France, Tirwhit entered Parliament for the first time. A year later, in the spring of 1417, he and Sir Richard Hansard (who was one of Justice Tirwhit’s leading supporters in his dispute with Lord Roos) were arraigned at Lincoln on an assize of novel disseisin, but they managed to avoid appearing in court. The prospect of foreign conquests took him abroad once more in the following July as a member of King Henry’s second expedition to Normandy. On this occasion he served with one mounted lance and three archers in the retinue of Robert, Lord Willoughby, for whom he was later to act as a trustee. The next four years were spent in France where he distinguished himself sufficiently to receive a knighthood and be made captain of three captured enemy castles.
Throughout this period Tirwhit was himself in some demand as a witness and feoffee-to-uses, attesting deeds for, inter alios, William, Lord Zouche, and Sir John Grey of Ingoldby. He was, moreover, involved in the property transactions of Sir William Oldhall and his wife, Margaret (Lord Willoughby’s sister), and he also became a trustee of the London jeweller, Lambert Waghtree.
Sir William’s last years were marked by two serious disputes as well as a lawsuit brought by him shortly before 1448 against a local man for trespass. Although hitherto perfectly amicable, his relations with (Sir) Thomas Cumberworth (who, as we have seen, was one of his trustees, and whom he likewise assisted in the same capacity) deteriorated somewhat as a result of rival claims to a watercourse which ran between their respective properties in Bigby. These claims were submitted, in 1447, to the arbitration of John, Viscount Beaumont, who recognized that despite the essentially trivial nature of their quarrel there was every likelihood of ‘debate and hevynes’ growing between the parties. The arbiter made an interim award, which was followed, three years later, by a more lasting compromise then achieved through the mediation of Bishop Lumley of Lincoln. Tirwhit was party to another private settlement reached at about this time, although the outcome proved far less satisfactory. On this occasion, he offered securities of 40 marks as a guarantee of his readiness to accept the award of four men who met at Beverley to determine the rights and wrongs of a quarrel with which he was then preoccupied. The arbitrators, who were evidently partial to his opponents, met secretly without informing his proxy, and then refused to surrender the bond he had given them. He sought redress in the court of Chancery, but the outcome is not recorded.