The family background and early life of Sampson Hardyng remain obscure, although he had already settled at Beadnell (a few miles south of Bamburgh castle on the Northumbrian coast) by 1374, when Alan Strother made him a grant of property there. Over the years Sampson extended his holdings in the area, acquiring farmland and tenements piecemeal, whenever the opportunity arose. In November 1383, for example, he purchased a substantial estate from the heirs of Sir Robert Coventry, thus adding considerably to his rent-roll. His first wife, Margaret, was, moreover, heir to an income of £5 p.a. from land in Heugh, Stamfordham and Ouston (to the west of Newcastle-upon-Tyne), and although the money was temporarily seized by the Crown in November 1375, an official inquiry eventually supported her title. Sampson maintained close connexions with the mercantile community in Newcastle-upon-Tyne, where he himself evidently did business. In November 1374 he stood surety in Chancery that the merchants Nicholas Haukeswell and William Deseburgh would ship hides only to designated ports along the east coast and not elsewhere; and three years later Deseburgh called upon him for similar guarantees regarding a cargo destined for London. The extent of his commercial ventures is now difficult to judge, although we know that he had less than successful dealings with Robert Hebburn, who managed to avoid paying him sureties of £78 for eight casks of woad. Sampson himself may have been obliged to borrow money from time to time to fund enterprises of this kind, for in 1375 he owed the parson of Thornton in Lonsdale 28 marks, and in the following year Robert Hales, the prior of the hospital of St. John of Jerusalem in England, a notorious usurer, advanced him £40 as a loan.
From 1375 onwards, when he was appointed to his first royal commission, Sampson devoted a growing amount of time to municipal and administrative business. In the beginning, his activities were centred largely upon Newcastle-upon-Tyne, where he served for many years as a collector of customs. He represented the town in six Parliaments between 1382 and 1397, as well as discharging two terms each as bailiff and mayor, and giving evidence there, in 1388, at the inquisition post mortem held on John, Lord Neville. His financial dealings suggest that he still had access to ready supplies of credit: in February 1383 he was able to stand bail of £400 for a group of local merchants, and not long afterwards Richard, Lord Scrope of Bolton, received from him bonds in a similar sum. Naturally enough, in view of his obvious flair for administration, his influence soon made itself felt throughout Northumberland as a whole, especially after his appointment, in 1382, to the county bench. In 1389, for instance, he was one of the small group of gentlemen chosen to settle a boundary dispute between the townships of Morpeth and Mitford; and in 1391 he became a feoffee of the manor of Gunnerston, which Sir Thomas Swinburne wished to settle in trust upon John Fenwick.
At about this time, Sampson obtained a royal licence for the alienation of rents worth four marks from property in Newcastle-upon-Tyne to the prior of Tynemouth. He may once again have been acting as a trustee rather than the actual owner of the land, as his own house lay in Pilgrim Street, and was leased by him, along with various appurtenances, at an annual rent of 46s.8d., from the influential Northumbrian landowner, Sir Thomas Gray.
As might be expected, Sampson not only represented Northumberland in Parliament but also had a hand in choosing other shire knights. He was present at the county elections of 1407, 1413 (May), 1417 and 1422, although, interestingly enough, his name always appears near the end of the list of witnesses to the return, among the lesser gentry, rather than at the beginning where his erstwhile parliamentary colleagues invariably took precedence.