Isaac Pendelton was born in King's County, Rhode Island (the former name for Washington County) on 22 November 1777.In 1802, he married Nancy Sheffield in Stonington, New London County, Connecticut. In October that year he was commissioned by Fanning & Coles as captain of the US ship Union and embarked on a sealing voyage to New Holland. In early 1803, Pendleton met French explorer, Nicolas Baudin in King George Sound.