The Mauleverer family had already been long established in Yorkshire when Sir John Mauleverer represented the county in the Parliament of 1334. A tireless campaigner against the Scots, he served on frequent commissions of array, and was also a j.p. in the West Riding. Halnath may well have been his great-grandson, although he did not inherit the widespread estates around Allerton Mauleverer which gave Sir John such an influential position in the community. His father, another Sir John, who died in November 1400, remains a shadowy figure, notable only for his involvement in two English expeditions to Scotland during the 1380s. Halnath must have come of age by March 1395, since it was then that he confirmed a grant of land in Rawdon and Horsforth made by his distinguished ancestor to Kirkstall abbey. An attempt to recover one of his villeins, whom he forcibly abducted from the city of York, brought him into direct confrontation with the mayor and aldermen at this time. His breach of the jealously guarded privilege of freedom from arrest earned him a reprimand in the civic court, in April 1397, and he was obliged to release the bondman at once.
Two years later, in June 1408, Sir Halnath and a group of his kinsmen, including Sir John Halnaby, obtained absolution from Archbishop Bowet of York for attending the clandestine marriage of Katherine Halnaby and Robert Place of Egton. Not long afterwards, the manor of Halnaby in Yorkshire, which was then held in dower by Katherine’s stepmother, was settled upon her in reversion with a remainder to the Mauleverers, although, so far as we know, Sir Halnath never obtained control of the property. He was, however, able to boast an impressive range of connexions, which now included the King’s younger son, John (later duke of Bedford), whom he indented to serve, in October 1408, for one year on garrison duty at Berwick-upon-Tweed. His own territorial base remained centred upon Whixley, Garrowby and North Deighton—all near York—and Ickeringill near Skipton in Craven. Wishing, no doubt, to concentrate his interests in one part of the county alone, he reached an agreement, in May 1411, whereby the more distant farmland in the West Riding was exchanged for tenements in the city of York itself.
In point of fact, Sir Halnath was preoccupied with far more mundane personal problems, as a result of his marriage to Millicent, the daughter of Sir Alexander Luttrell. The land in North Deighton which comprised her jointure had been held in trust for some time by a local man named Robert Mauger, and,although unsuccessful in the long term, his attempts to contest her title caused considerable annoyance. Having already served on at least three royal commissions in the West Riding, Sir Halnath was finally returned to Parliament for Yorkshire in 1419, and appointed sheriff of the county one year later. He relinquished office in April 1422, after which date no more is heard of him, save that he died at some point before March 1433. His eldest son, John, is said to have inherited his estates.