William Cushing was born to a old and distinguished Massachusetts family. He was a teacher for a year following graduation from Harvard College. He then turned to law and established a private practice in Scituate, his home town. But he was not a skilled lawyer and left practice for the bench. He served as a justice of the peace and as a judge of probates in the region of Massachusetts now known as Maine, but he seemed incapable of making decisions, which is a necessary condition of judging. (Cushing was the last American judge to wear a full wig. He abandoned the habit in 1790.)
Cushing was a reluctant supporter of revolution in the colonies. But he was a strong advocate of the new Constitution. He was vice president of the state ratifying convention in 1788.
Washington nominated Cushing as one of the original Supreme Court appointees. While still on the High Court, Cushing ran unsuccessfully against Samuel Adams for governor of Massachusetts. Washington offered Cushing the chief justice position when Jay resigned, but Cushing declined.