Around 1715, Jennings operated as a privateer from Jamaica, working for the governor Archibald Hamilton. He was commissioned to captain the Barsheba, an eight gun and eighty man vessel that would be part of Hamilton's privateer fleet. Jennings hired the idle and cruel sailor Charles Vane to his crew, and learned that the Spanish Treasure Fleet had wrecked off the coast of Florida.
With the war over, Jennings turned to piracy, committing the first of these acts in early 1716. He had gathered the most feared and cruel group of pirates in the West Indies, and attacked the Spanish fleet's salvage camp. He divided 150 of his men into three companies, each led by a drummer and a flag bearer. They outnumbered the Spanish troops three to one, and the commander, Don Francisco de Salmon, was forced to surrender and give up the location of the wrecks.
Jennings teamed up with Samuel Bellamy and Paulsgrave Williams to commit piracies against the French later that year. After the group had captured the frigate St. Marie, Bellamy and Williams fled with most of the plunder, and sought protection with fellow pirate Benjamin Hornigold, who had a hostile relationship with Jennings. While Jennings drank and whored in Nassau, a group of pirates led by Vane claimed the remainder of the loot aboard the St. Marie.
Jennings soon became a leading figure in the Pirate Republic of Nassau, along with Hornigold, Edward Thatch and Vane.