After the death of Peyto’s father in 1407, his mother married John Knightley, who secured young William’s wardship and marriage at the Exchequer. In 1415 Knightley arranged his marriage to one of the daughters of Sir Robert Francis, and the couple were given possession of part of William’s inheritance: Sowe (Warwickshire) and Great Wyrley (Staffordshire). His mother, who subsequently married the wealthy Sir Robert Corbet of Hadley, retained the rest of his estates until her death in 1418. In 1436 Peyto’s landed holdings were estimated to be worth £150 a year, a sum which probably included the profits from lands acquired through his second marriage, to Katherine Gresley, whose dower from Thomas Stafford, her previous husband, included Aston and Campden in Gloucestershire and Sibbertoft in Northamptonshire.
Peyto was to make his mark as a military commander in the English occupation of northern France. Early in 1420 his name was placed on a list of 13 sent by the Warwickshire j.p.s to the King’s Council in response to a request for information about those best able to defend the realm, and for the time being he evidently remained in England. He sat in the House of Commons, apparently for the only time, later that year and attended the shire court for the elections to the next Parliament (May 1421). But it was not long before he embarked on his first campaign in France, where he took part in the battle of Cravant in July 1423. Later that year Peyto was retained for life by Richard, earl of Warwick, from whom he received an annuity of 20 marks. As a member of Warwick’s affinity he was associated with (Sir) William Mountfort I and John Throckmorton in making a settlement on Richard Curson (later to be the earl’s chamberlain and executor), and from 1429 he acted as a feoffee when the earl purchased the reversion of the Grovebury priory estates from the countess of Salisbury (a task which he and his co-feoffees finally relinquished in 1445 when they transferred their interest to Eton college). Meanwhile, he had sought election to the Parliament of 1427, adopting unscrupulous means to achieve his purpose: Mountfort and John Mallory had already been elected when Peyto arrived in Warwick at the head of a local mob and, with the connivance of the under sheriff, managed to secure the substitution of his own name on the electoral indenture in place of Mallory’s. Nevertheless, it seems likely that the outcry against these bullying tactics permitted Mallory to take his seat. When sheriff himself, in 1429, Peyto made the return for Warwickshire of Mountfort and Thomas Hugford, both of whom were his fellow retainers of the earl of Warwick.
By the summer of 1443 Peyto had joined the army of John Beaufort, duke of Somerset, encamped at Tréport and Fécamp, and had been appointed by him as commander of some 450 men ‘de bonne estoffe’, who were ordered to occupy a ‘bastille’ built by the English on a hill outside Dieppe in order to cut off supplies to the French in the town as well as to launch an attack. The siege collapsed in August in the face of an assault by the Dauphin, and despite a valiant defence the ‘bastille’ was taken by superior numbers. Peyto was captured and held to an ‘intolerable ransom’ of 3,000 écus (about £500). During his imprisonment his wife suffered a two-pronged assault on her property: an attack on her manor of Campden, for which a group of men associated with John, Lord Beauchamp of Powick, was responsible, and the theft of cattle from Sibbertoft perpetrated by the notorious Sir Thomas Mallory (son of Peyto’s one-time opponent at the hustings). To obtain his release Peyto apparently first looked to the executors of Somerset’s uncle, Thomas Beaufort, duke of Exeter, for a loan of 500 marks, and it was doubtless to repay this that on his return to England in the winter of 1445-6 he mortgaged his estates. Those who then came to his aid included Sir William Mountfort and his own wife’s father, Sir John Gresley, and uncle, John Curson, it being agreed that Peyto should reimburse them all before Michaelmas 1448. Peyto’s financial position was, however, made even worse by the failure of the Crown to pay him his wages of war. In May 1447 it was ordered that certain tallies worth £266 13s.4d., issued in his name at the Exchequer in the previous year, should be freshly assigned; but although the urgency of the case was made clear, he was evidently still unable to secure payment, and more new tallies of assignment had to be issued in 1450.
Although Peyto had managed to recover Sowe and Wyrley, and had settled them on his son, John, he had been unable to retrieve Chesterton, for which he still needed £120 in 1460. Indeed, at the time of his death, on 24 Nov. 1464, Chesterton was in the hands of his creditors, and it took three more years for his heir to obtain possession.