He served as the head coach for two teams in the National Football League (NFL), the Los Angeles Rams from 1966 to 1970 and the Washington Redskins from 1971 to 1977.

Seven of his teams qualified for the NFL playoffs, including the 1972 Washington Redskins, who reached Super Bowl VII, losing to Don Shula's Miami Dolphins.

His eldest son, also named George Allen, is a Republican politician who served as Governor of and United States Senator from Virginia.

His second son, Bruce, followed his father's footsteps as a football coach and executive, serving as general manager for the Tampa Bay Buccaneers and the Redskins of the NFL.

Allen's presence also had a formative effect on such future Hall of Fame players as linebacker Bill George and end Doug Atkins during their most productive years.

Following their 14–10 victory over the New York Giants on December 29 at frigid Wrigley Field, the Bears' players awarded Allen the "game ball."

Jeff Davis's biography Papa Bear states that Halas informally told Allen in 1964 and 1965 that he would ultimately name him as head coach.

But in 1965, after a 9–5 Bears finish that earned the iron-willed Halas NFL Coach of the Year honors, Allen decided to look elsewhere to fulfill his head-coaching ambitions.

The Bears' owner did win his case in a Chicago court but immediately allowed Allen to leave, saying he initiated the lawsuit to make a point about the validity of contracts.

Allen brought his well-known motivational skills to Los Angeles, and his twice-daily (sometimes three times) rigorous training-camp practices took players by surprise.

Allen received 1967 Coach of the Year honors for leading the Rams to an 11–1–2 record and the NFL Coastal Division title, their first post-season berth since 1955.

After the favored Rams struggled to a tie at San Francisco, Allen disparaged the sloppy Kezar Stadium turf; a few days later Reeves, addressing reporters, subtly admonished his coach for making what he considered an "alibi."

"[7] Allen's firing was met not only with criticism from fans and reporters,[citation needed] but an overwhelming show of support from Ram players: 38 members of the team's 40-man roster, including such standouts as Gabriel, Jones, Olsen, Lundy, Dick Bass, Jack Snow, Bernie Casey, Tom Mack, Irv Cross, Ed Meador, and Jack Pardee, stated for the record that they would seek a trade or retire if Allen were not reinstated.

Allen and the 1969 Rams seemed to justify the coach's renewed presence; their 11–3 record earned them a Coastal Division title as Gabriel won the NFL's Most Valuable Player award.

It had been tacitly assumed that Allen had been granted the two extra years to bring the Rams a title, and so the second time the firing met with neither fan outrage nor player objection.

Allen quietly left Los Angeles as the most successful coach in Rams history; he is currently fourth on the franchise's all-time wins list behind John Robinson, Chuck Knox, and Mike Martz.

[8] Shortly after joining the Redskins, Allen made a series of trades with his former Ram team and brought seven 1970 Los Angeles players to Washington, including the starting linebacker corps (Maxie Baughan, Myron Pottios, and Pardee).

Becoming a household phrase among NFL fans was the "Over-the-Hill Gang"—the aging Redskin veterans who seemed to save their best efforts for the most important games.

As had been the case with the Rams, Allen's intense approach was seen to indicate that winning in the present was all-important, with planning for the franchise's future taking a lesser priority.

[9][10] He was replaced by one of his favorite players, Jack Pardee, by then the promising young head coach of the Bears, who had gained the wild card playoff berth ahead of the Redskins; both had finished at 9–5.

Rams owner Carroll Rosenbloom was searching for a new coach after parting ways with Chuck Knox, and decided to bring Allen back.

He thus worked with general manager Don Klosterman to oversee a talented roster that had made the team a perennial playoff challenger.

As newspaper reports were quoting players expressing confidence that differences would be resolved, the Rams played listlessly and lost the first two games of the 1978 exhibition schedule.

In his first season in 1983, the Blitz were tabbed as the early favorite to capture the league's inaugural title, in part because Allen assembled a roster laden with NFL veterans.

[14] Allen's need for full organizational control and his wild spending habits would create friction between him and the team owners he worked for.

In ending Allen's second stint as the Rams' head coach after only two preseason games in 1978, Carroll Rosenbloom said, "I made a serious error of judgment in believing George could work within our framework."

He even went as far as being the first coach in the NFL to employ a full-time security man, Ed Boynton, to keep potential spies away and patrol the woods outside Redskin Park.

It is interesting to note that President Richard Nixon (an armchair coach) once "recommended" the team run an end-around play by wide receiver Roy Jefferson.

[16] During Allen's early years with the Redskins, the team was known as the "Over-the-Hill Gang," due to the predominance of players over the age of 30, such as quarterback Billy Kilmer.

Levy led the Buffalo Bills to four consecutive Super Bowl appearances in the early 1990s, while coaching perhaps the greatest special teams coverage man ever, Steve Tasker.