A lawyer employed by Hull for his counsel, John appears to have had family links with the town, since Robert de Killingholme was one of the bailiffs in 1391-2.
On 27 Jan. 1449 Killingholme was one of four nominees put forward by the aldermen of Hull for election to the first Parliament of that year, whereupon the commonalty chose him and the mayor, Hugh Clitheroe*, to represent them in the Commons.
Just over two years after the dissolution of the Parliament, Killingholme was appointed common clerk and recorder of Kingston-upon-Hull, with an annual fee of £4 and 3½ ells of cloth for his robes. His brief tenure of these offices was almost certainly due to ill health, since he made his will on 9 Sept. 1452. He sought burial in St. Mary’s church at Hull and provided for a modest funeral and the holding of obits there. Killingholme settled his property in the town on his only child, his daughter Katherine. In the event of her death without heirs, his executors were to sell it and employ the proceeds for the benefit of his soul. He left the remainder of his goods to his widow, asking her to use them to settle his debts and for further charitable purposes. Katherine was among those whom he named as an executor, for which role he also chose two fellow townsmen, Thomas Patrikton and Thomas Sproxton. Probate was granted on 1 May 1453.
