Shortly after World War II, three veterans of the New Deal founded the law firm then known as Arnold, Fortas & Porter. Thurman Arnold was a former Yale Law School professor, Assistant Attorney General, and US Court of Appeals Judge. Abe Fortas, who would later become a Supreme Court Justice, also served in various government positions, including as Undersecretary of the Interior. Paul Porter was a former Chairman of the Federal Communications Commission and Administrator of the wartime Office of Price Administration.

Thurman Arnold, a brilliant, iconoclastic lawyer and economist, endowed the firm with its institutional ambition to confront and find creative answers to complex legal issues. Abe Fortas contributed a meticulous and uncompromising emphasis on technical excellence, and Paul Porter, a quintessential "Washington lawyer," infused the firm with a tradition of independence and originality. They were three very different people who together gave the firm they founded an appreciation and respect for individuality.

These principles and the personalities of Arnold & Porter's founders still shape the firm today. Many of the firm's attorneys have held senior positions in the White House and in such US government agencies as the Departments of State and Justice, the Federal Reserve Board, the Federal Trade Commission, the Federal Communications Commission, and the Securities and Exchange Commission. Several attorneys, both partners and associates, teach part-time at law schools, and many write for legal and business publications. Many also participate in national and local bar association activities as well as in continuing legal education programs.