As a young man, William Carnaby entered the service of John of Gaunt, who made him constable and receiver of Dunstanburgh shortly before February 1372, and also retained him as a member of his affinity. Besides performing the usual administrative duties, Carnaby had to execute various commissions for the duke. Not long after assuming office, for example, he was ordered to effect major repairs to the castle, and also, at about the same time, to hold a formal inquiry regarding certain complaints from the prior of Finchale in Durham.
William’s improved financial prospects no doubt enabled him to negotiate an extremely advantageous marriage with Margaret, the daughter and sole heir of Sir Henry ap Griffith, whose wardship had passed on the death of her widowed mother, in 1381, to John, Lord Neville. Margaret brought her new husband the manor of Nether Witton and other widespread holdings in the Northumbrian villages of Stannington, Benton, Bellasis, Wingates and Tranwell, but they cannot have remained in his hands for more than a short time. Her early death, in 1387, at the age of just 17, before she had produced an heir, meant that the property reverted to her young cousin, Thomas ap Griffith, and was thus lost to William. Perhaps in memory of his late wife, he made a gift of land in Highfield to the priory of Hexham, although before long he was busy negotiating another marriage with Sir Henry Fenwick, a local landowner, who offered him the hand of his daughter Isabel. William and the Fenwicks were already comrades in adversity, having suffered at the hands of Sir Robert Ogle, who had imprisoned the former and seized cattle from the latter on the ground that they owed him money. William’s fortunes seem to have been at an unusually low ebb during this period, for he had barely escaped from Ogle’s clutches when his estates around Halton were devastated by a band of marauding Scots and he himself was carried off across the border as a hostage. King Richard promised a contribution of 100 marks to secure his release, although when finalized, in December 1390, the royal grant merely exempted him from paying an annual charge of £4 which the Crown had previously demanded from him as a feudal tenant. Since William claimed to have been ruined by the raid, the King’s offer did little to solve the immediate problem of raising a substantial loan, but somehow the Scots were paid off, and William obtained his freedom. Although probably exaggerated, his losses must indeed have been considerable, as the evidence of his inquisition post mortem, held many years later in 1408, reveals. Even then his three manors were producing no more than £12 6s.8d. because of the damage done by the Scots.
Although he served loyally on a few royal commissions during the reign of Richard II, and helped to defend both Jedburgh and Berwick-upon-Tweed against the Scots during the late 1380s, William did not really assume a position of trust on the east march until after the Lancastrian usurpation of 1399. In this respect, his career was remarkably similar to that of his brother-in-law, Robert Hebburn, one of the leading figures in the local mercantile community, who clearly shared his sympathies. As a former retainer of Henry IV’s father, John of Gaunt, William in particular came in for his share of patronage, and in 1401 Bishop Skirlaw of Durham bestowed on him the five offices which together gave him almost complete authority in the episcopal liberty of Norhamshire and Islandshire. Having restored his finances to a state of equilibrium, he was able, in June 1403, to purchase half the manor of Saddlingstones, and this, too, was entailed upon his elder son. Not surprisingly, by the date of his first and only known return to Parliament, in the following year, he had assumed the rank of knight; and he was seen as an ideal candidate for the stewardship of Hexhamshire when it fell vacant a few months later. But Sir William was already well advanced in years and had little time in which to enjoy his new career. He died in May 1407 while in office as escheator of Northumberland, having just confirmed the entails which he had previously made upon his elder son. The latter became the ward of Robert Tempest, a northern landowner who married the widowed Isabel Carnaby within a few months of Sir William’s death. Isabel herself died in 1411, so that when he came of age in the following year William Carnaby the younger took immediate possession of all the family estates. He played an active part in local society, becoming steward of Hexhamshire, like his father before him, and marrying (as his second wife) a daughter of Robert, Lord Hilton. He had at least one brother, named Thomas, and a sister, who eventually became the wife of her first cousin, Thomas Hebburn of Newcastle.