In 1931, Hein signed a contract with the New York Giants, married his college sweetheart, and packed all of their belongings into a 1929 Ford and drove from Pullman to New York. He played for 15 years as a center and a defensive lineman. Hein was a first-team All-Pro center eight straight years from 1933 to 1940. He was also selected as the NFL's most valuable player in 1938. He was the starting center on two NFL championship teams — in 1934 (NYG 30, Chicago 13) and again in 1938 (NYG 23, Green Bay 17). Hein was also a member of five Giants teams that lost NFL championship games — 1933, 1935, 1939, 1941, and 1944.