Jaybien was probably a Cornishman by birth. In the early 15th century he owned well over 200 acres of land in Liskeard, ‘Nether Trenant’ Lansallos, ‘Kylgalyn’ and Stratton, in Cornwall; but he acquired property in Devon, too, at Huish, Little Modbury and Plymouth, and it was here, at Plymouth, that he chose to reside, perhaps in his house off Bilbury Street. In 1420 he made a quitclaim of all of his lands in the neighbourhood of Liskeard, apart from a croft which he had given to John Coles, and he may then have left that area for good because of his unpopularity there. Not long before he had presented a petition in Chancery against Sir Ralph Botreaux and his followers for eviction and assault, but he himself had exacerbated the situation by securing the release from Lostwithiel gaol of one of his assailants and secreting him away, so that it was feared that the man had been done to death.
This incident was the only serious blot on the reputation of an able lawyer whose services in the administration and conveyance of landed estates were evidently in great demand. Although Jaybien did occasionally appear as an attorney in the central courts at Westminster, his main sphere of activity was in the West Country. Early in his career, in 1404, he was asked by Richard Spicer I to assist him in making settlements of his property, and shortly afterwards the powerful head of the Bonville family, Sir William, entrusted him and other feoffees with eight manors and a tin-works for a term of 80 years. In the course of the next few years Jaybien was party to transactions concerning the holdings in Devon and Dorset of Sir John Prideaux and William Mountfort II, the wealthy Bridport merchant, and such dealings brought him into close contact with the chief justice, Sir William Hankford, and Sir Humphrey Stafford II of Hooke. After his only known return to Parliament, in 1411, he occasionally attended the shire elections held at Exeter castle, being named on the electoral indentures drawn up in 1413, 1414, 1419, 1421, 1427 and 1433.
Jaybien was appointed to many royal commissions concerning west country affairs, his presence often being specifically required for those of a judicial nature. In 1414, for example, he was not only instructed to investigate lollard activity in Devon and to confer with eminent doctors of law about a judgement made in the court of admiralty, but also to preside over assizes of novel disseisin. When Henry Fulford, the escheator of Devon and Cornwall, died in May 1420, Jaybien took over the post and performed his duties competently in the course of his two-year term of office, although he was afterwards sued in Chancery by Nicholas Bachelor of Modbury for failing to restore moveables worth nearly £10 which he had allegedly confiscated in error. For a few months, as successor to Sir John Fortescue and predecessor of John Copplestone, Jaybien served as steward of the estates of Hugh Courtenay, earl of Devon, after whose death, in 1422, he took on the responsibility of authorizing expenditure by the estate staff. In the same year Thomas Stonor asked him to arbitrate between him and Richard Fortescue in their dispute over tenancy of the manor of Ermington, Devon; and in the 1420s and 1430s his services in similar or other respects were sought by several prominent local figures, including John Crocker of Lyneham, Sir John Herle†, (Sir) John Arundell I and Walter Bodulgate, the last named requiring his help when founding a chantry at Camelford. From December 1428 until May 1429 Jaybien shared with John Hody and Nicholas Aysshton, the future judges, a royal grant of part of the Pomeroy inheritance, and it was also with Aysshton that, in 1432, he presented to the church of St. Stephen in Brannel, Cornwall. Jaybien’s patronage of the churches of Drewsteignton and Week St. Mary was similarly part of the responsibilities entailed in the trusteeship of local estates.
Jaybien failed to sit on two royal commissions, dated 17 and 18 Nov. 1436, but this was clearly the result of an error, for he swore an oath before Bishop Lacy of Exeter that he had never received the letters patent of appointment. Indeed, he was generally conscientious in the execution of such commissions, and it is perhaps surprising that he was not appointed to the bench until 1438. One of his last recorded acts was to arrange a settlement for Richard Trenode, the Bristol merchant who, in 1439, did much to obtain Plymouth’s charter.
Jaybien’s will, made on 1 Dec. 1441, was not granted probate until February 1447, and the precise date of his death is not known. Among his bequests were law books and several robes trimmed with fur, one of which had been a gift from Bishop Lacy. He was buried in St. Andrew’s church, Plymouth, before the altar in the aisle dedicated to St. John the Baptist, which he himself is thought to have had built. It was there that Jaybien’s chantry was afterwards founded.