American consultant who helped establish public relations as a recognized profession.

In high school Byoir was a reporter for the Iowa State Register, and by the age of 17 he was city editor of the Waterloo Tribune. He worked his way through the University of Iowa, went to work for the Hearst magazines, and by 1916 had become circulation manager of Cosmopolitan. During World War I he was called to Washington as an associate chairman of the Committee on Public Information and thus helped lead the U.S. government's propaganda effort in that conflict.

After the war, health problems led him to Cuba, where he grew interested in promoting U.S. tourism to Cuba, and this led to a contract with the government of the dictator Gerardo Machado, and the establishment of Byoir's firm, Carl Byoir and Associates, in New York City in 1930.

In 1938 Byoir counseled the Great Atlantic and Pacific Tea Company, a grocery chain, and directed a public relations campaign that eventually defeated in Congress a tax bill that chain-store owners considered ruinous. This won him the enmity of the powerful U.S. representative Wright Patman of Texas, a militant “trust buster,” and led to Byoir's conviction in 1946 of violating the Sherman Antitrust Act.

At the start of his involvement in public relations that craft was scarcely distinguishable from press agentry, but in the course of his career Byoir's emphasis on organization, planning, and effective action contributed significantly to its increasing professionalism.