Yeo was ordered by Smith to bring dispatches to a Portuguese general from whom he learned of French privateers based at Cayenne, French Guiana. On 6 January 1809, he took command of a small force consisting of "Confiance", two Portuguese brigs, and 550 Portuguese soldiers. With them he captured Cayenne, a fortified position of two hundred guns, and took a thousand prisoners. The conquest of French Guiana would remove the French from their last South American colony. During the operation, Yeo was among the many British who became sick. In 1810, he was knighted for his services at Cayenne, both by the Portuguese who decreed him a member of the Order of Aviz and the British, who decreed him a knight commander of the Order of the Bath and was given his own coat-of-arms. Yeo was the first Protestant to be made a member of the Order of Aviz.