Cohan was born in Providence, Rhode Island to Irish Catholic parents. A baptismal certificate (which gave the wrong first name for his mother) indicated that he was born on July 3, but the Cohan family always insisted that George had been "born on the Fourth of July!" George's parents were traveling Vaudeville performers, and he joined them on stage while still an infant, at first as a prop, later learning to dance and sing soon after he could walk and talk.

He completed a family act called "The Four Cohans", which included his father Jeremiah "Jere" Cohan (1848-1917), mother Helen "Nellie" Costigan Cohan (1854-1928), and sister Josephine "Josie" Cohan Niblo (1874-1916).

Josie's husband, Fred Niblo Sr. (1874-1948) was an important director of silent films, including Ben Hur (1925), and was a founder of the Academy of Motion Picture Arts and Sciences. Their son, Fred Niblo Jr. (1903-1973) was an Academy Award-nominated screenwriter.

By his teens, Cohan became well-known as one of Vaudeville's best male dancers, and he also started writing original skits and songs for the family act. Soon he was writing professionally, selling his first songs to a national publisher in 1893. Cohan had his first big Broadway hit in 1904 with the show Little Johnny Jones, which introduced his tunes "Give My Regards to Broadway" and "The Yankee Doodle Boy".

Cohan became one of the leading Tin Pan Alley songwriters, publishing upwards of 1500 original songs, noted for their catchy melodies and clever lyrics. His other major hit songs included "You're a Grand Old Flag", "The Warmest Baby In The Bunch", "Life's A Funny Proposition After All", "I Want to Hear a Yankee Doodle Tune", "You Won't Do Any Business If You Haven't Got A Band", "Mary's a Grand Old Name", "The Small Town Gal", "I'm Mighty Glad I'm Living, That's All", "That Haunting Melody", and the very popular war song, "Over There".

His 1936 song "Johnny Q. Public of the U.S.A." popularized a new nickname for the average citizen. An avid baseball fan, he also composed the official march of the St. Louis Cardinals.

Cohan was the pioneer of the musical theater libretto. He is mostly remembered for his songs, later interpolated into musicals such as Anything Goes, Guys and Dolls, The Producers, and Hello Dolly! However, he invented the "book musical," becoming the first showman to bridge the gaps between drama and music, operetta and extravaganza.

More than three decades before Agnes De Mille choreographed Oklahoma!, Cohan used dance not merely as razzle-dazzle but to advance the plot. The engaging books of his musicals supported the scores that yielded so many popular songs. As a storyteller, Cohan's main characters were "average Joes and Janes".

Characters like Johnny Jones and Nellie Kelly appealed to a whole new audience. He wrote for every American, instead of highbrow Americans. (see book by Thomas S. Hischak, Boy Loses Girl (ISBN 0-8108-4440-0).

In 1914, he became one of the founding members of ASCAP. In 1919, he unsuccessfully opposed a historic strike by Actors' Equity Association, for which many in the theatrical professions never forgave him. During the strike, he donated $100,000 to finance the Actors' Retirement Fund in Englewood Cliffs, New Jersey.

Cohan wrote numerous other Broadway musicals and straight plays, in addition to contributing material to shows written by others — more than 50 in all. Cohan shows included Forty-five Minutes from Broadway (1905), George Washington, Jr. (1906), The Talk of New York and The Honeymooners (1907), Fifty Miles from Boston and The Yankee Prince (1908), Broadway Jones (1912), Seven Keys to Baldpate (1913), The Cohan Revue of 1918 (co-written with Irving Berlin), The Tavern (1920), The Rise of Rosie O'Reilly (1923, featuring a 13-year-old Ruby Keeler among the chorus girls), The Song and Dance Man (1923), American Born (1925), The Baby Cyclone (1927, one of Spencer Tracy's early breaks), Elmer the Great (1928, co-written with Ring Lardner), and Pigeons and People (1933).

He earned acclaim as a serious actor in Eugene O'Neill's Ah, Wilderness! (1933), and in the role of a song-and dance President Franklin D. Roosevelt in Rodgers and Hart's musical, I'd Rather Be Right (1937).

His final play, The Return of the Vagabond (1940) featured Celeste Holm in the cast; she was either 21 or 23 years old at the time.

In 1925, Cohan published his autobiography, Twenty Years on Broadway and the Years It Took to Get There.

In 1932, Cohan starred in a dual role (as a cold, corrupt politician and his charming, idealistic campaign double) in the Hollywood musical The Phantom President, co-starring Jimmy Durante and Claudette Colbert, with songs by Rodgers and Hart.

In 1940, Judy Garland played the title role in a film version of his 1922 musical, Little Nellie Kelly. Cohan's mystery play, Seven Keys to Baldpate, was first filmed in 1916 and has been remade seven times, most recently as House of the Long Shadows (1983), starring Vincent Price.

His 1920 play The Meanest Man in the World was filmed with Jack Benny in 1943.

In 1942, a musical biopic of Cohan, Yankee Doodle Dandy, was released, and James Cagney's performance in the title role earned the Best Actor Academy Award. The film was privately screened for Cohan as he battled the last stages of abdominal cancer.

He died on November 5, 1942, at his New York City home, 993 5th Avenue, directly across the street from the Metropolitan Museum of Art, aged 64, from the cancer that he had battled.

After a large funeral at St. Patrick's Cathedral on Fifth Avenue, Cohan was interred at the Bronx's Woodlawn Cemetery, in a private family mausoleum he had erected a quarter-century earlier for his sister and parents.

Cohan is probably the most honored American entertainer. In 1941, President Franklin Delano Roosevelt presented him with a Congressional Gold Medal in honor of his contibutions to World War I morale, in particular the songs "You're a Grand Old Flag" and "Over There".

In 1959, at the behest of composer Oscar Hammerstein II, a $100,000 bronze statue of Cohan was dedicated in Times Square, at Broadway and 46th Street in Manhattan.

The 8-foot bronze remains the only statue of an actor in New York City. He was inducted into the Songwriters' Hall of Fame in 1970, and into the American Folklore Hall of Fame in 2003.

His star on the Hollywood Walk of Fame is located at 6734 Hollywood Boulevard. The United States Postal Service issued a 15-cent commemorative stamp honoring Cohan on the anniversary of his centenary in July 1978.

Many of these honors were accepted posthumously by Cohan's large family. In 1899, he had married Ethel Levey (1881-1955), a musical comedy actress who bore him a daughter, Georgette Cohan Souther Rowse (1900-1988). George and Ethel divorced in 1907 and she spent much of her subsequent career in England.

He married again in 1907 to Agnes Mary Nolan (1883-1972), who had been a dancer in his early shows; they remained married until his death. They had two daughters and a son. Mary Cohan Ronkin (1909-1983) had a brief career as a cabaret singer in the 1930s, and later composed a score for her father's non-musical play The Tavern, and in 1968 supervised musical and lyric revisions for the Broadway play George M!.

Helen Cohan Carola (1910-1996) made several movies, including Lightnin (1930) starring Will Rogers, and was one of the WAMPAS Baby Stars of 1934.

George M. Cohan, Jr. (1914-2000) graduated from Georgetown University and served (along with Sammy Davis Jr.) in the entertainment corps during World War II.

In the 1950s, George Jr. reinterpreted his father's songs on recordings, in a nightclub act, and in television appearances on the Ed Sullivan and Milton Berle shows. George Jr.'s only child, Michaela Marie Cohan (1943-1999), was the last descendant named Cohan. She graduated with a theater degree from Marywood College, Scranton, Pennsylvania, in 1965.