Born in Mahanoy Plane, Pennsylvania, Thomas Francis Dorsey Jr. was the second of four children born to Thomas Francis Dorsey Sr., a bandleader, and Theresa (née Langton) Dorsey.
He and Jimmy, his older brother by slightly less than two years, became known as the Dorsey Brothers. The two younger siblings were Mary and Edward, who died young.
Tommy Dorsey studied the trumpet with his father but later switched to trombone.
At age 15, Jimmy recommended Tommy to replace Russ Morgan in the Scranton Sirens, a territory band in the 1920s. Tommy and Jimmy worked in bands led by Tal Henry, Rudy Vallee, Vincent Lopez, and Nathaniel Shilkret. In 1923, Dorsey followed Jimmy to Detroit to play in Jean Goldkette's band and returned to New York in 1925 to play with the California Ramblers.
In 1927, he joined Paul Whiteman. In 1929, the Dorsey Brothers had their first hit with "Coquette" for OKeh Records.
In 1934, the Dorsey Brothers band signed with Decca, having a hit with "I Believe in Miracles". Glenn Miller was a member of the Dorsey Brothers Orchestra in 1934 and 1935, composing Annie's Cousin Fanny, Tomorrow's Another Day, Harlem Chapel Chimes, and "Dese Dem Dose", all recorded for Decca, for the band. Acrimony between the brothers led to Tommy Dorsey walking out to form his own band in 1935 as the orchestra was having a hit with "Every Little Moment".Dorsey's orchestra was known primarily for its renderings of ballads at dance tempos, frequently with singers such as Jack Leonard and Frank Sinatra.
Dorsey was married three times. His first wife was 16-year-old Mildred "Toots Kraft, with whom he eloped in 1922, when he was 17. The couple had two children, Patricia and Thomas F. Dorsey III (nicknamed "Skipper"). In 1935, they moved to "Tall Oaks", a 21-acre (8.5 ha) estate in Bernardsville, New Jersey. They divorced in 1943 after Dorsey's affair with his former singer Edythe Wright.
Dorsey's second wife was film actress Patricia Dane in 1943, and they were divorced in 1947, but not before he gained headlines for striking actor Jon Hall when Hall embraced her.
Finally, Dorsey married Jane Carl New on March 27, 1948, in Atlanta, Georgia. She had been a dancer at the Copacabana nightclub in New York City. Tommy and Jane Dorsey had two children, Catherine Susan and Steve.