He graduated from Yale University in 1767. He then studied law with Judge Titus Hosmer in Middletown, was admitted to the bar and practiced law in Farmington.
On November 20, 1770, John Treadwell married Dorothy Pomroy, of Northampton, Massachusetts. He was then elevated to the governor"s council. He held that position until 1783.
He was elected to the Confederation Congress in 1784, 1785, and 1787, but did not attend.
From 1786 to 1797 he served as Judge of the Court of Common Pleas. In 1788 he was a Delegate to the state convention that ratified the United States Constitution.
In 1789 Treadwell became Judge of the Probate Court and the Supreme Court of Errors, serving until 1809. In 1798, Treadwell was elected the Lieutenant Governor of Connecticut, an office he also held until 1809.
Jonathan Trumbull, the Governor of Connecticut, died in office on August 7, 1809.
Treadwell, lieutenant governor at the time, assumed the governor"s office. He was elected by popular vote on April 9, 1810, to the governorship. During his term, the Hartford Fire Insurance Company was proposed, and the Non-Intercourse Acting was reinstated in February 1811, which resulted from Connecticut"s opposition to the United States"s impeding war with Great Britain.
Treadwell left office on May 9, 1811 after an unsuccessful re-election bid.
In 1814-1815 he was a Connecticut delegate to the Hartford Convention. Treadwell, a Congregationalist, died in Farmington, Hartford County, Connecticut, on August 18, 1823 (age 77 years, 268 days).
He is interred at Farmington Old Cemetery.
American Academy of Arts and Sciences]
Treadwell served as a member of the General Assembly from 1776 to 1783. He was a member of Connecticut council of assistants from 1786 to 1798. He was a member of the 1818 Constitutional Convention and also served on the American Board of Commissioners for Foreign Missions.