Hales was the eldest son of Sir Thomas Hales, 3rd Baronet, a long-serving Member of Parliament who held a series of lucrative posts in the Royal Household. He succeeded to his father's baronetcy on 6 October 1762. Earlier the same year, he had entered Parliament as a member of Downton, a pocket borough under the control of his brother-in-law Lord Feversham. He initially supported the government, but in February 1764 he voted with the opposition over the use of general warrants in the Wilkes case, and seems to have been henceforth regarded as of doubtful loyalties.
He did not stand for re-election in 1768, but returned to the Commons at a by-election at Dover in January 1770, as the government-backed candidate, and remained its MP for the remaining three years of his life.
He married Mary Heyward, daughter of Gervase Heyward of Sandwich, in 1764, and they had five daughters:
Mary Anne Hales (born 1765)
Jane Hales (born 1766), married Henry Bridges (1769–1855), who later changed his name to Brook
