The name "Brehon" is anglicized from the Irish "breitheamh". The word breitheamh is derived from the word breith, meaning "judgment". The Brehon Laws are the oldest known European laws. The Brehons of ancient Ireland were wise men of the family who memorized and applied the laws to settle disputes among members of the family.

The Philadelphia Brehon Law Society is a professional association organized to foster the profession of law among individuals of Irish ancestry. The Society is comprised of Judges, lawyers and law students and their friends. Brehon was chosen as the original name of the Society when it was founded in 1976 by among others, Honorable Joseph P. McCabe and Thomas A. White., Jr.

The Society provides forums for educational, cultural and social activities concerning Irish heritage and tradition. The Society also seeks to promote closer affiliations between the bench, the bar, students of law and the community, and to further a high standard of legal ethics.

Since the time the Society was founded, it has grown from a handful of lawyers to over 500 members and now has branches in law schools in the Delaware Valley area, including Villanova University School of Law, Temple University Beasley School of Law, Rutgers School of Law - Camden, Drexel University Earle Mack School of Law and Widener Law School.

The Society counts many members of the judiciary among its members including Chief Justice Ronald D. Castille and,Justice Seamus McCaffery of the Pennsylvania Supreme Court.