 He became a merchant in Barbados until about 1764, when he moved back and became a partner in the firm of Ridgely, Howard & Lux, and was involved with the Ridgely family ironworks.Prior to 1773, Darby was a dealer in convict servants from America to the West Indies, and a partner in the rum importing business with William Russell, brother of James Russell (1708–1788) in London.Lux also became involved in a lead mining operation in Baltimore County.