A prominent and wealthy merchant, Middleton owned a considerable amount of property in Southampton. By 1389 he was in possession of Bull Hall in Bull (Bugle) Street, adjacent to a site on which he had a 60-year lease from the hospital called God’s House, a messuage, two shops in St. Michael’s parish and a tenement in English Street. In 1397 he purchased plots of land along with annual rents amounting to £11, and in the next year he conveyed two tenements and a garden on the east side of English Street to a fellow merchant, Walter Lange. Then, in 1404, he acquired premises in French Street.
Although there is no record of his appointment, Middleton was apparently serving as customer of Southampton as early as 1386, when he was ordered to release a consignment of wine belonging to a merchant of Bayonne which he had unjustly confiscated. His own mercantile activity involved him in the wool trade, and when, in 1407, it was decided that the wool beam should be moved from West Hall, because the customers were unable to see the ‘Woolbridge’ from there, a royal inquiry established that Middleton’s new house was the most suitable alternative, being the ‘largest and strongest’ of all the merchant dwellings and, in any case, situated opposite the bridge. In July 1408 he joined with Thomas Armorer in lending £200 to the earl of Kent, on security of much plate and jewels. Two years later, Middleton’s construction of a wharf and crane at the ‘Watergate’ upset the merchants of Salisbury and Winchester, who indignantly complained that, hindered thereby from landing their goods at the gate, they were having to pay double rates for carriage from the ships into the town. Middleton took the profits of wharfage and cranage by assent of the municipal authorities, to whom they remained after his death.
This successful entrepreneur was often asked to act as a feoffee of local property, as an attorney at liveries of seisin and as an executor. In the last-named capacity he served for some 15 years in the administration of the estate of John Polymond†, one of Southampton’s most prominent merchants, and later for two other burgesses, John Barflete and John Renaud (a former mayor); but he refused to undertake the executorship of the will of Richard Bradway. His connexions outside Southampton were few, but sometimes of considerable distinction: for instance, in 1405 he found surety at the Exchequer for Eleanor, Lady St. Amand, (Sir) John Pelham and John Kirkby II, the lessees of the estates of Thomas, late Lord West. Mayor for as many as four terms, Middleton also served, in November 1424, as deputy for the then mayor, William Soper.
Meanwhile, in August 1420, Middleton and his second wife had obtained an indult from Pope Martin V allowing them to have a portable altar. He probably died late in 1428, for although in September that year £10 13s.4d. was paid to him by the town ‘pour son anuelte’, in the following year this sum was handed to his executors.