Arnold established himself in business in 1762 as a pharmacist and bookseller in New Haven, Connecticut, with the help of the Lathrops. He was hardworking and successful, and was able to rapidly expand his business. In 1763, he repaid money that he had borrowed from the Lathrops, repurchased the family homestead that his father had sold when deeply in debt, and re-sold it a year later for a substantial profit. In 1764, he formed a partnership with Adam Babcock, another young New Haven merchant. They bought three trading ships, using the profits from the sale of his homestead, and established a lucrative West Indies trade.