He engaged in classical studies at the college in the English Colony of Rhode Island and Providence Plantations (now known as Brown University), graduating in 1770.

[3][4] Foster was a protege of Brown University's first chancellor, Chief Justice of Rhode Island and Providence Plantations and revolutionary patriot Stephen Hopkins.

[5] Foster married the sister of the future governor of Rhode Island and Providence Plantations Arthur Fenner.

[6] Foster played a role in the Gaspee Affair of 1772, along with John Brown and others, which helped catalyze events leading to up to the American Revolutionary War.

Rhode Island's state legislature re-elected him in 1791 and 1797, and he served until March 3, 1803, when he retired from public life to engage in writing and historical research.

[9] Foster returned to public life to serve in the Rhode Island state legislature from 1812 to 1816.