From 1920-1931 the NFL championship was determined by a team's won-loss percentage. In 1932, a playoff game was arranged following the season to determine the championship.

1920 - Akron Pros
1921 - Chicago Staleys
1922 - Canton Bulldogs
1923 - Canton Bulldogs
1924 - Cleveland Bulldogs
1925 - Chicago Cardinals
1926 - Frankford Yellow Jackets
1927 - New York Giants
1928 - Providence Steam Roller
1929 - Green Bay Packers
1930 - Green Bay Packers
1931 - Green Bay Packers
1932 - Chicago Bears

1933 was the first year that the NFL played a championship game

1933 - Chicago Bears
1934 - New York Giants
1935 - Detroit Lions
1936 - Green Bay Packers
1937 - Washington Redskins
1938 - New York Giants
1939 - Green Bay Packers
1940 - Chicago Bears
1941 - Chicago Bears
1942 - Washington Redskins
1943 - Chicago Bears
1944 - Green Bay Packers
1945 - Cleveland Rams
1946 - Chicago Bears
1947 - Chicago Cardinals
1948 - Philadelphia Eagles
1949 - Philadelphia Eagles
1950 - Cleveland Browns
1951 - Los Angeles Rams
1952 - Detroit Lions
1953 - Detroit Lions
1954 - Cleveland Browns
1955 - Cleveland Browns
1956 - New York Giants
1957 - Detroit Lions
1958 - Baltimore Colts
1959 - Baltimore Colts

The American Football League operated from 1960 through 1969

1960 - Houston Oilers (AFL)
1960 - Philadelphia Eagles (NFL)
1961 - Houston Oilers (AFL)
1961 - Green Bay Packers (NFL)
1962 - Dallas Texans (AFL)
1962 - Green Bay Packers (NFL)
1963 - San Diego Chargers (AFL)
1963 - Chicago Bears (NFL)
1964 - Buffalo Bills (AFL)
1964 - Cleveland Browns (NFL)
1965 - Buffalo Bills (AFL)
1965 - Green Bay Packers (NFL)
1966 - Green Bay Packers (NFL)

The AFL and NFL announced that the two leagues would merge in 1970. The Super Bowl started to determine the world champions. The game featured the champion of each league.