In 1376 during the minority of Ingrid and Margaret, daughters of John Giffard, custody of the latter’s lands was assigned to Colyn’s father John (afterwards sheriff of Cornwall in 1387-8 and 1391-2), who immediately arranged the marriage of the elder girl to his son. As a result of this marriage, Thomas Colyn acquired substantial properties in Cornwall, including the manors of Helland and Helset, and the advowsons of Helland and St. Pinnock, and it was probably he who rebuilt the manor-house at Helland. In right of his wife he occasionally acted as co-patron of the benefice of Roseash, Devon.2J. Maclean, Trigg Minor, ii. 7, 36-37, 415; Cornw. Feet of Fines, 891; Reg. Brantingham ed. Hingeston-Randolph, 99; Reg. Stafford, 177, 322; CPR, 1494-1509, p. 274 (where he is incorrectly said to have married Margaret Giffard).
Colyn’s father had served Thomas Beauchamp, earl of Warwick, as steward of his estates in Cornwall, and he himself made important contacts among the gentry of the shire: at the elections for the January and September Parliaments of 1397, for example, he was asked to provide securities for the knights-elect, John Colshull I and John Arundell I. On as many as five occasions he was appointed as a collector of parliamentary subsidies, including those granted by the Commons of which he was a Member (in 1402). Colyn may also have had something to do with the administration of the duchy of Cornwall, of which the borough of Launceston formed a part, for in June 1404, together with John Skewys and two others, he entered into recognizances for £24 to the then holder of the duchy, Henry of Monmouth, the prince of Wales. He also acted as a surety at the Exchequer for the prior of St. Michael’s Mount in 1403, when he was granted custody of the priory estates. Three years later he appeared at the assizes at Launceston as guardian of his kinsman Robert Colyn alias Brune, putting the latter’s claim to be the true heir of Sir William Brune†.3C219/9/12, 13; CCR, 1399-1402, p. 398; CFR, xii. 200; Maclean, iii. 123; JUST 1/1519 m. 86; Harl. Ch. 76B 6. Colyn had been serving as a coroner of Cornwall at the time of his only known return to Parliament. However, in May and November 1409, after he had held office for about nine years, writs were sent to the sheriff ordering his replacement because he was insufficiently qualified. This did not prevent his re-election in 1411 and his continued tenure of the post for a further nine years. It was just before his re-appointment that, described as Thomas Colyn ‘esquire’, he took out a royal pardon of outlawry for his failure to appear in court to answer the suit of a London draper for debt. Colyn was party to the elections of the knights of the shire for Cornwall held prior to the Parliaments of 1407, 1411, 1413 (May), 1414 (Nov.) and 1417. In November 1420 he was said to be too sick and aged to continue his duties as coroner, and it may well have been shortly afterwards that he died.4CPR, 1408-13, p. 250; C219/10/4, 6, 11/1, 4, 12/2; CCR, 1419-22, p. 94. In the following spring his son John (who had married the daughter of John Nicoll of Bodmin, Thomas’s fellow Member in the Parliament of 1402), represented Lostwithiel in the Commons.