William Cushing was a judge of the first rank under three sovereigns — the province, the commonwealth, and the nation. Born in 1732 into a Massachusetts family of judges, he succeeded his own father on the province's highest court, and when revolution came he was the only member of that court to side with the patriots — keeping his seat when the new Commonwealth reconstituted it.
His most consequential act came before his federal career began. In Commonwealth v. Jennison (1783), a criminal assault case arising from an owner's attempt to recapture a man he claimed as a slave, Cushing charged the Worcester jury that slavery was incompatible with the new Massachusetts constitution: "our Constitution of Government... sets out with declaring all men are born free and equal... and in short is totally repugnant to the idea of being born slaves." There was no statute. No legislature acted. Slavery ended in Massachusetts by judicial interpretation alone — in 1783, eighty years before the Thirteenth Amendment.
He kept the Massachusetts courts open during Shays' Rebellion when armed mobs surrounded the courthouse — bayonets rapping on his chest, face blanched, step firm — then presided over the rebels' treason trials. He was the pivotal figure at the Massachusetts ratification convention. Washington made him one of the original six justices in 1789.