Williams was born in 1761 or 1762, the son of Naval Captain William Williams. Aged only 7, Thomas Williams was entered as a servant on his father's ship , although it is likely that he did not spend much time aboard. He is reported to have followed his father through various commands (although many of these commissions were on paper only) until 1776, when he was certainly present at the Battle of Sullivan's Island, aboard the brig . The following year he moved to , flagship of Rear-Admiral Samuel Barrington in the Caribbean. "Prince of Wales" was subsequently engaged at the Battle of St. Lucia in 1778 and the Battle of Grenada in 1779. Having gained the requisite seniority, Williams was promoted to lieutenant in December 1779 and served on , part of the fleet that captured a Spanish convoy from Caracas in 1780. Returning briefly to Britain, Williams returned to the Americas the following year with Vice-Admiral Marriott Arbuthnot and fought at the Battle of Cape Henry.