Thomas was born in St John's and came from a line of merchant mariners from Devon, England.
Thomas's shipping operations brought him along a triangular route that included Britain, the Caribbean and Newfoundland.
According to Prowse:...officials and merchants vied with each other in creating country residences and farms [...] finest of all, Brookfield, the property of William and Henry P.
As a very young man he was secretary to the society for improving the condition of the poor; he was equally distinguished as a merchant and a politician.
Brookfield, the fine house at Devon Row, their Water Street premises, and the beautiful cottage at Topsail, are monuments to the large progressive ideas of the Thomases, and especially of the constructive ability of Henry Phillips Thomas.