Grantham may have been a descendant of John Grantham, who was assessed at a modest 6d. to the parliamentary tenth levied in Leicester in 1354, and of William Grantham, admitted to the town’s merchant gild in the 1360s.
Grantham’s frequent appearance in the legal records suggest that he was one of the more substantial of the town’s burgesses, and his office-holding career confirms this. After serving as one of the bailiffs in 1431-2, he went on to hold office both as mayor and as one of the four stewards of the fair. While holding the latter office, he was, on 16 Oct. 1449, elected to represent the borough in Parliament with his fellow steward, Adam Racy.
It is likely that Grantham did not long survive his only recorded appearance in Parliament, the last session of which met in his home town and ended in early June 1450. The last reference to him occurs in the following month: on 20 July he witnessed a charter for William Wymondeswold*, with whom he had served as bailiff nearly 20 years before.
