It seems likely that Thomas came of a local family, for John Lavyngton, a fishmonger, and Michael Lavyngton, a tailor, were both resident in Reading in the 1370s, and Robert Lavyngton was perhaps mayor in 1410-11.
Nevertheless, during the period in which he represented Reading in Parliament, Lavyngton accumulated land and property elsewhere in Berkshire. In 1429 he and his wife took possession from their kinsman, John Polton, of property in Maidenhead and Windsor, and in later years he acquired additional holdings, including two farms at Cookham. As one of the gentry of the shire he attended the county court at Abingdon for the election of the Berkshire representatives to the Parliament of 1432, and two years later he was required, along with other local notables, to take the generally administered oath against maintenance of breakers of the peace.
Over the years Lavyngton made the acquaintance of other influential members of the local gentry. In 1424 he had acted as a feoffee on behalf of William Perkins, and, like Perkins, in the late 1440s he came to be associated with William de la Pole, marquess of Suffolk, Sir Edmund Hungerford and others in buying land in Berkshire on behalf of John Norrys. The latter, one of the most successful of Lancastrian courtiers, obtained with the assistance of these associates substantial estates in the county, some of which were either held jointly with Hungerford and Lavyngton, or placed in their trust. When, in 1447, Norrys obtained the keeping of the lordship of Cookham and Bray, Lavyngton appeared at the Exchequer as one of his mainpernors. It seems likely that Lavyngton’s connexion with the courtier was that of legal advisor. Clearly, he owed his appointment to the county bench, late in life, to a reputation based on service to such as Norrys and the abbot of Reading (for whom he had earlier acted in an undefined way in the conduct of suits against debtors).