John Blair Jr. (April 17, 1732 – August 31, 1800) was an American Founding Father, who signed the United States Constitution as a delegate from Virginia and was appointed an Associate Justice on the first U.S. Supreme Court by George Washington.

He was devoted to the idea of a permanent union of the newly independent states and was a loyal supporter of fellow Virginians James Madison and at the Constitutional Convention.

They had a large family, with ten or twelve children by various accounts, and John was the fourth child, and the eldest surviving son.

James Blair, had founded and become the first president of the College of William & Mary, and at his death bequeathed much of his estate to this man's father.

Returning home to practice law, Blair was admitted to the Virginia bar in 1757 and quickly thrust into public life.

He began his public career shortly after the close of the French and Indian War with his election to the seat reserved for the College of William and Mary in the House of Burgesses (1766–1799).

He opposed Patrick Henry's extremist resolutions in protest of the Stamp Act, but the dissolution of the House of Burgesses by Parliament profoundly altered his views.

[5] In 1786, the legislature, recognizing Blair's prestige as a jurist, appointed him Thomas Jefferson's successor on a committee revising the laws of Virginia.

[4] On September 24, 1789, President George Washington nominated Blair for one of the five associate justice positions on the newly established U.S. Supreme Court.