In 1650, upon learning that the Spanish had evacuated St. Croix, de Poincy dispatched his officer Vaugelan with two ships and 160 men to seize control of the island. The French forces set fire to the dense forests, which had previously hindered Spanish settlement efforts, to facilitate their own colonization. ​

Subsequently, in 1651, de Poincy persuaded the Grand Master of the Knights of Malta, Giovanni Paolo Lascaris, to purchase several Caribbean islands—including St. Croix—from the bankrupt Compagnie des Îles de l’Amérique. The Knights acquired St. Croix, Saint Kitts, Saint Barthélemy, and Saint Martin, with de Poincy continuing to govern these territories on their behalf until his death in 1660. ​

While de Poincy may not have resided permanently on St. Croix, his actions were instrumental in bringing the island under the control of the Knights of Malta and establishing their brief colonial presence in the Caribbean.