 His first judicial service was on the Supreme Court of Errors when it was established in 1785, but he soon shifted to the Connecticut Superior Court and spent four years on its bench.Ellsworth participated in the 1787 Constitutional Convention in Philadelphia as a delegate from Connecticut along with Roger Sherman and William Samuel Johnson.More than half of the 55 delegates were lawyers, eight of whom, including both Ellsworth and Sherman, had previous experience as judges conversant with legal discourse.