Hein next played fifteen seasons in the NFL as a center for the New York Giants from 1931 to 1945. He was selected as a first-team All-Pro for eight consecutive years from 1933 to 1940 and won the Joe F. Carr Trophy as the NFL's Most Valuable Player in 1938. He was the starting center on NFL championship teams in 1934 and 1938 and played in seven NFL championship games (1933–1935, 1938–1939, 1941, and 1944).