At the age of 15, Larkin went to Boston to apprentice as a bookbinder but decided against the business. In 1821 he sailed to Wilmington, North Carolina, where he worked as a clerk and experienced a disastrous partnership with a dishonest merchant. He visited Bermuda in 1822 and relatives in New England in 1824. In 1825 he opened a store in Duplin, North Carolina. The fortune he made on the store he lost on a sawmill operation, and in 1830 he returned to Massachusetts, destitute. Here he learned that his half-brother, John Bautista Rogers Cooper, needed his assistance with a business in California, and in September 1831 Thomas left Boston on the ship "Newcastle". After a stopover in the Sandwich Islands (Hawaii), he landed in San Francisco, in April 1832.