Halas, born in Chicago, Illinois into a family of Czech immigrants, had a varied career in sports. After graduating from Crane Tech High School in Chicago, he attended the University of Illinois, playing football for coach Bob Zuppke as well as baseball and basketball, and earning a degree in civil engineering. He helped Illinois win the 1918 Big Ten football title. Serving as an ensign in the Navy during World War I, he played for a team at the Great Lakes Naval Training Station, and was named the MVP of the 1919 Rose Bowl. On a team which included Paddy Driscoll and Jimmy Conzelman, Halas scored two touchdowns and returned an intercepted pass 77 yards in a 17-0 win; the team was also rewarded with their military discharges.

Afterward, Halas played minor league and semi-pro baseball. He was so good at baseball, he eventually earned a promotion to the New York Yankees, where he played 12 games as an outfielder in the major leagues in 1919. However, a hip injury effectively ended his baseball career. He was replaced in the outfield by the legendary Babe Ruth.

Offered a position with a Decatur, Illinois starch manufacturer as a company representative, player on the company-sponsored baseball team, and player-coach of the football team by company founder A.E. Staley, Halas selected the University of Illinois' colors - orange and blue - for the team's uniforms. In 1920, Halas represented Decatur at the meeting which formed the National Football League in Canton, Ohio, and was awarded a franchise he called the Decatur Staleys, in honor of the founder's financial contribution. After suffering financial losses despite a 10-1-2 record, the club moved to Chicago in 1921, winning the NFL championship that year. They took the name Bears in 1922 as a tribute to the Chicago Cubs, who permitted the Bears to play their games at Wrigley Field.

With the Staleys and Bears, Halas not only played offensive end but also handled ticket sales and the business of running the club; lore says he even sold tickets before the game. All of that perhaps not being enough to do, Halas also coached the team. Named to the NFL's all-pro team in the 1920s, his playing highlight occurred in a 1923 game when he stripped Jim Thorpe of the ball, recovered the fumble, and returned it 98 yards - a league record which would stand until 1972. In 1925, Halas persuaded Illinois star player Red Grange to join the Bears; it was a significant step in establishing both the respectability and popularity of the league, which had previously been viewed as a refuge for less admirable players.

After ten seasons, Halas stepped back from the game in 1930, retiring as a player and leaving the sidelines as coach; but he remained the owner of the club, becoming sole owner in 1932. The lure of the field was too much, however, as Halas returned in 1933 to coach the Bears for another ten seasons. During his absence from coaching, the team had also won the 1932 championship. His 1934 team was undefeated until a loss in the championship game to the New York Giants.

In the late 1930s, Halas - with University of Chicago coach Clark Shaughnessy - perfected the T-formation system to create a revolutionary and overwhelming style of play which drove the Bears to an astonishing 73-0 victory over the Washington Redskins in the 1940 NFL Championship Game. Every other team in the league immediately began trying to imitate the format. The Bears repeated as NFL champions in 1941, and the 1940s would be remembered as the era of the "Monsters of the Midway".

Halas and Shaughnessy had created a revolutionary concept with the T-formation offense. The complex spins, turns, fakes and all around athletic versatility required to execute the scheme, limited the possible players available. Halas recruited Columbia University quarterback Sid Luckman in 1939. Luckman launched his Hall of Fame career, playing the position from 1939 to 1950. Halas was not satisfied with other players that succeeded Luckman. During this coaching stint, he had on the Bears roster two future Hall of Fame players, Bobby Layne in 1948 and George Blanda from 1949 to 1958. Other notable players included Heisman Trophy winner Johnny Lujack from 1948 to 1951 and Zeke Bratkowski from 1954 to 1960. Blanda played in the NFL until 1975; Bratkowski moved on to Vince Lombardi's Green Bay Packers from 1960 to 1971; and Bobby Layne quarterbacked the Detroit Lions to three NFL championship games between 1952-54, winning two.

Halas went on a second three-year hiatus during World War II, serving in the Armed Forces from 1943-45, while the Bears won another title in 1943. Returning to the field in 1946, he coached the club for a third decade, again winning a title in his first year back as coach. After a brief break in 1956-57, he resumed the controls of the club for a final decade from 1958 to 1967, winning his last championship in 1963. He did not, however, enjoy the same success as he had before the war. He did win his 200th game in 1950 and his 300th game in 1965, becoming the first coach to reach both milestones. In 40 years as a coach, he endured only six losing seasons.

Halas played an integral part in the segregation of the league in the 1930s by refusing to sign black players for the Bears. Fritz Pollard, who in the 1920s was the league's first African-American coach, blamed Halas for keeping him out of the league in the 1930s and 1940s. Halas eventually changed course and helped to integrate the league, drafting the NFL's first black player since 1933, George Taliaferro, although Taliaferro did not play for the Bears; Halas later signed Willie Thrower, who with the Bears became the league's first black quarterback.

A pioneer both on and off the field, Halas made the Bears the first team to hold daily practice sessions, to analyze film of opponents to find weaknesses and means of attack, place assistant coaches in the press box during games, and to broadcast games by radio. He also offered to share the team's substantial television income with teams in smaller cities, firmly believing that what was good for the league would ultimately benefit his own team. A firm disciplinarian, Halas maintained complete control of his team and did not tolerate disobedience and insubordination by players. He also insisted on absolute integrity and honesty in management, believing that a handshake was sufficient to finalize a deal; few, if any, intermediaries were necessary.

After the 1967 season, Halas - then the oldest coach in league history - retired as coach. He continued to own the club and to be involved in business decisions. He was honored in 1970 and 1980 as the only person involved in the league throughout its first fifty and sixty years of existence.

George Halas' career ledger reads as follows: 63 years as an owner, 40 as a coach, 324 wins, and 8 NFL titles as a coach or owner. He was a charter member of the Pro Football Hall of Fame in 1963; the Hall of Fame is appropriately located on George Halas Drive. The NFC championship trophy also bears his name. In both 1963 and 1965 he was selected by The Sporting News, the AP and the UPI as the NFL Coach of the Year. In 1997 he was featured on a US postage stamp as one of the legendary coaches of football. He has been recognized by ESPN as one of the ten most influential people in sports in the 20th century, and as one of the greatest coaches. In 1993, Miami Dolphins coach Don Shula finally surpassed Halas' victory total. To this day, the jerseys of the Chicago Bears bear the initials "GSH" on their left sleeves in tribute to Halas.

In the 1971 made-for-television film Brian's Song, about the friendship between Chicago Bears players Brian Piccolo and Gale Sayers, Halas was portrayed by Jack Warden, who won an Emmy Award for his performance.

Halas died of cancer in Chicago on October 31, 1983 at age 88, and is entombed in St. Adalbert Catholic Cemetery in Niles, Illinois. His eldest daughter, Virginia, remains involved with the Bears in their front office.