John was perhaps the grandson of the John Sumpter of Colchester who was born in about 1331. His father, another namesake, was a .successful attorney, acting for many clients in the courts at Westminster in the 1380s and 1390s and being especially closely connected with Sir Thomas Swinburne. Indeed, his fraudulent dealings in a case involving Swinburne’s manor on Mersea island resulted in a petition to the Parliament of 1391. It was probably Sumpter senior who was admitted as a freeman of Colchester in 1396-7 and who obtained a papal indult for plenary remission at death in 1398.
Sumpter’s marriage to one of the daughters of Sir Geoffrey Brokholes and grand daughter of Sir John Roos (d.1373), led to the acquisition by his children of a substantial landed estate: a moiety of the combined Brokholes and Roos holdings, which comprised the manors of Giffards in Great Sampford, Roos in Radwinter and New Hall in Asheldham (Essex), Rooshall in Sarratt, Brokholes in Great Munden and Overhall in Gilston (Hertfordshire), and Brokholes in Mancetter (Warwickshire). When Sumpter’s mother-in-law died in 1419, the moiety of these estates then inherited by his young son, John, was granted in wardship to John Leventhorpe, the receiver-general of the duchy of Lancaster. The other moiety passed to his sister-in-law Joan, widow of Thomas Aspall, for whom he subsequently stood surety when she undertook not to remarry without the King’s permission. Young John died in 1421, leaving as his heirs his sisters, Christine (b.1411) later the wife of Thomas Bernard, and Ellen (b.1413), later the wife of James Bellers, whose godparents included such local worthies as Christine, wife of Thomas Godstone, Mary, widow of Simon Fordham, and the prior of St. Botolph’s, Colchester. Their inheritance remained in the Crown’s possession until 1427 when most of it was divided between them, but their attempts to obtain the property in Warwickshire from their aunt, a few years later, brought forth allegations that they were both bastards.
Sumpter’s marriage had enhanced his standing in the shire, so much so that, in 1417, he had been associated with Joan de Bohun, countess of Hereford (of whom some of the properties due to be inherited by his son were held) in transactions regarding certain manors in Essex. He found considerable employment as a feoffee-to-uses to a number of prominent local landowners, including Sir William Argentine and Sir William Coggeshall, and at the parliamentary elections held in Hertfordshire towards the close of 1421 he provided securities for the appearance in the Commons of Sir Philip Thornbury. He had established an especially close relationship with Robert Tey, the former constable of Colchester castle and his alleged fellow conspirator against Henry IV, for whom he performed the services of a feoffee and eventually an executor.
Sumpter is not recorded alive after Hilary term 1432, when he was named with Lewis Robessart, Lord Bourgchier, as a feoffee of East Newland, Essex, probably on behalf of the late Thomas Godstone.