In 1946, Cowan joined the firm established by Henry C. Rogers. In 1950, he became a partner in the firm, which then changed its name to Rogers & Cowan. He was named president in 1964. Rogers & Cowan became one of the largest entertainment public relations firm in the world handling not only entertainers but also high-tech manufacturers, athletes, publishers, movie studios and trade unions. Whenever he was asked to name his favorite client, Cowan's constant answer was always "the next one."