John Blair Jr. was born in Williamsburg in 1732 into one of Virginia's most prominent families. His father served on the Governor's Council for decades and was four times acting Governor; his great-uncle, the Reverend James Blair, founded William & Mary and served as its first president. (Do not confuse the three — it is the Supreme Court justice who has no biographer.) He studied at William & Mary, read law at the Middle Temple in London, married in Edinburgh in 1756, and returned to Virginia for a career of steady, distinguished public service. He was not the type to seek the spotlight.
What sets Blair apart is how early his judicial instincts led him toward constitutional principle. In 1782, on the Virginia Court of Appeals in Commonwealth v. Caton, he joined in establishing that courts could annul legislative acts inconsistent with the constitution — a direct precursor to Marbury v. Madison two decades later. At the Constitutional Convention he was one of only three Virginia delegates to sign the finished document. At the Virginia Ratification Convention of 1788 he worked quietly for approval. Washington, who prized him, made him one of the original six justices.