Comparatively little evidence has survived about Harper’s early life. He is said to have been the son of one John le Harpur and Isabel, the daughter of Sir Robert Appleby, but this cannot now be proved. The earliest known reference to him occurs in August 1411, when he appeared as an attorney at the Stafford assizes.
In October 1420, Harper joined with Joan, the widow of Sir Thomas Harcourt, and others in acquiring the wardship and marriage of Sir Thomas’s young heir from the Crown, although the award was subsequently revoked on the ground that Sir John Wilcotes had already received custody of the boy. The estates of the late Thomas Bromley, esquire, were also awarded to Harper at this time, again on what proved to be little more than a temporary basis.
Harper’s early success clearly owed much to his influential connexions. In July 1422 and February 1426 he stood surety at the Exchequer for, respectively, the above-mentioned Lady Abergavenny and Henry Bourgchier, count of Eu (later earl of Essex).
By the date of his election as a shire knight, if not well before, Harper had acquired a considerable amount of property. Besides the scattered and mostly short-term grants of land made to him in the early 1420s, he either bought or inherited a fishery at Ashley in Staffordshire while still a young man. According to a series of transactions begun in November 1422, Harper seems over the years to have gained possession of the manors of West Tilbury in Essex, Henhurst in Kent and Pontefract (‘Pountfreit’) in Middlesex. These had previously belonged to John and Katherine Falk, whose son, Nicholas, later made a conveyance of his Shropshire estates to Harper, almost certainly as a feoffee-to-uses. Perhaps the Falks had initially intended to mortgage rather than sell their holdings in the south-east, but whatever their motives at least one of the three manors was still in the hands of Harper’s descendants in 1471.
There can be little doubt that Harper’s real influence as a landowner was due to his marriage to Eleanor, the daughter and heir of William Grobbere. This brought him a substantial estate in the Rushall area, although it also involved him in yet more lawsuits, some of which may have been collusive. From 1430 onwards Harper and his wife consolidated their holdings in this part of Staffordshire. In 1438 they obtained a royal charter of free warren on their demesnes there, and soon afterwards they were awarded royal letters patent permitting them to endow a perpetual chaplaincy which was to be held by their own nominee. Harper had previously been at odds with the abbot of Halesowen over the right of presentation, but their dispute was settled amicably enough, and the MP even donated a composite volume of religious texts to the abbey. In July 1446 Harper secured confirmation from Henry VI of all the franchises in Rushall which he and his wife had fought so hard to recover.
Although his chief allegiance lay with the Staffords, Harper also became associated with other members of the English baronage. In February 1434, for instance, he acted as a mainpernor with the earl of Suffolk for his friend, Thomas Mulsho, while at the same time attempting to recover a debt of £20 owed jointly to him and William, Lord Zouche. Four years later he stood surety at the Exchequer for John Sutton, Lord Dudley. By 1442, the earl of Shrewsbury had engaged him as an auditor, and in 1453 he was one of the trustees of Richard, earl of Warwick.
Harper died on 3 July 1464 and was buried in the church of the Grey Friars at Lichfield. He left two sons, William and Richard, both of whom maintained their father’s connexion with the house of Stafford. Richard possessed a similar aptitude for law and finance, rising to become an official at the receipt of the Exchequer, and eventually receiver-general of the duchy of Lancaster. In May 1474 he obtained permission from Edward IV to endow a chantry at Swinford in Leicestershire in memory of his parents.