Eugene Volokh on a Jury of One's Peers:
Jury of one's peers: One hears a lot about how people are entitled to "a jury of their peers," and how this-and-such trial is unfair because the jurors weren't really the defendant's peers in some significant way (race, class, or what have you). What does the law really say about the right to trial by jury of one's peers?
Well, U.S. law actually uses this phrase pretty rarely -- it doesn't appear in the U.S. Constitution, Bill of Rights, or statutes -- and for good reason. In England, the phrase apparently referred to a right of nobles to be generally tried by nobles, and commoners by commoners.
Dan Klerman, who teaches law at USC and who is an expert on (among other things) English legal history, puts it this way, ":Basically everyone got jurors from the same pool, except members of the House of Lords ("peers"), who were tried by the House of Lords itself."
The concept does make for great drama in Dorothy L. Sayers' novel Clouds of Witness. Here, her detective - Lord Peter Wimsey - defends his brother - The Duke of Denver - who has been accused of murder and faces a trial in the House of Lords.