Born in East Greenwich in the Colony of Rhode Island and Providence Plantations, Tillinghast was elected as a member of the Rhode Island House of Representatives and served from 1772 to 1773.
He held several offices under the Revolutionary authorities and again served in the Rhode Island House of Representatives from 1778 to 1780.
He served as an associate justice of the Rhode Island Supreme Court from May 1781 to May 1787, and again from May 1791 until his resignation in December 1797.
Tillinghast died in East Greenwich, Rhode Island on August 26, 1821.
Interment was in Tillinghast Lot (Rhode Island Historical Cemetery East Greenwich #18) located on South County Road, East Greenwich.