In 1765, Charles Winstone entered Gray's Inn in London for the study of law, and 13 years later, on August 8, 1778, King George III appointed him the attorney general of Dominica, an office which he held for several years. During this time, he managed absentee estates, as well as his own plantation, on which several hundred slaves produced coffee and other crops. As the American Revolution made trade with Europe nearly impossible, Winstone contemplated a move to nearby St. Kitts or Antigua. In 1780, he was appointed solicitor general of Antigua and settled there in September 1781. In 1783, when the British reclaimed control of the island from the French and conditions became more favorable to trade, he returned to Dominica. He lived there until at least 1795.
Sometime before 1770, Winstone married Antigua-born Rachel Ireland, daughter of John Ireland and Rebecca Bacon. The Winstones had one child Rebecca who survived to maturity.