At an early age he attracted the attention of Henry Collins, a wealthy merchant and philanthropist, who decided to fund Southwick's college education.
He quickly suspended publication of the Mercury and fled with his family, remaining in Providence, Rhode Island and Rehoboth, Massachusetts until it was safe to return home.
In 1778 he was appointed Deputy Commissary General, responsible for obtaining and distributing food, clothing and other supplies to Continental Army soldiers in Rhode Island.
In addition to publishing the Mercury, Southwick's printing business included the production of notes that were used as currency by America's fledgling banking industry.
They had four sons and a daughter, and their children included Solomon Southwick (1773-1839), a prominent newspaper publisher in Albany, New York and founder of the Anti-Masonic Party.