Hamlisch was born in Manhattan, to Viennese-born Jewish parents Lilly (née Schachter) and Max Hamlisch. His father was an accordionist and bandleader. Hamlisch was a child prodigy, and, by age five, he began mimicking the piano music he heard on the radio. A few months before he turned seven, in 1951, he was accepted into what is now the Juilliard School Pre-College Division.  His first job was as a rehearsal pianist for Funny Girl with Barbra Streisand. Shortly afterward, he was hired by producer Sam Spiegel to play piano at Spiegel’s parties. This connection led to his first film score, The Swimmer. His favorite musicals growing up were My Fair Lady, Gypsy, West Side Story, and Bye Bye Birdie. Hamlisch attended Queens College, earning his Bachelor of Arts degree in 1967.

Although Liza Minnelli’s debut album included “The Travelin’ Life,” a song he wrote in his teens (originally titled “Travelin’ Man”), his first hit did not come until he was 21 years old. This song, “Sunshine, Lollipops, and Rainbows”, co-written with Howard Liebling, was recorded by Lesley Gore and reached #13 on the Billboard Hot 100 in the summer of 1965. His first film score was for The Swimmer, after the film’s producer Sam Spiegel hired Hamlisch based on a piano performance Hamlisch did at a party. Later he wrote music for several early Woody Allen films such as Take the Money and Run and Bananas. In addition, Hamlisch co-wrote the song “California Nights” (also with Liebling), which was recorded by Lesley Gore for her 1967 hit album of the same name. The Bob Crewe-produced single peaked at #16 on the Hot 100 in March 1967, two months after Gore had performed the song on the Batman TV series, in which she guest-starred as an accomplice to Julie Newmar’s Catwoman.

Among his better-known works during the 1970s were adaptations of Scott Joplin’s ragtime music for the motion picture The Sting, including its theme song, “The Entertainer”. It hit #1 on Billboards Adult Contemporary chart and #3 on the Hot 100, selling nearly 2 million copies in the U.S. alone. He had great success in 1973, winning two Academy Awards for the title song and the score for the motion picture The Way We Were and an Academy Award for the adaptation score for The Sting. He won four Grammy Awards in 1974, two for “The Way We Were”. In 1975, he wrote what, for its first 12 years, would be the original theme music for Good Morning America—it was built around four notes. He co-wrote “Nobody Does It Better” for The Spy Who Loved Me (1977) with his then-girlfriend Carole Bayer Sager, which would be nominated for an Oscar. In the 1980s, he had success with the scores for Ordinary People (1980) and Sophie’s Choice (1982). He also received an Academy-Award nomination in 1986 for the film version of A Chorus Line. His last projects included The Informant! (2009), starring Matt Damon and directed by Steven Soderbergh.  Prior to his death, he completed his first children’s book Marvin Makes Music, which included the original music “The Music in My Mind” with words by Rupert Holmes, and the score for the HBO film Behind the Candelabra (2013), also directed by Soderbergh and starring Damon and Michael Douglas as Liberace.

Hamlisch’s first major stage work was in 1972 playing piano for Groucho Marx at Carnegie Hall for An Evening with Groucho. Hamlisch acted as both straight man and accompanist while Marx (at age 81) reminisced about his career in show business. The performances were released as a 2-record set, and remained very popular.  He then composed the scores for the 1975 Broadway musical A Chorus Line, for which he won both a Tony Award and a Pulitzer Prize; and for the 1978 musical They’re Playing Our Song, loosely based on his relationship with Carole Bayer Sager.

At the beginning of the 1980s, his romantic relationship with Bayer Sager ended, but their songwriting relationship continued. The 1983 musical Jean Seberg, based on the life of the real-life actress, failed in its London production at the UK’s National Theatre and never played in the U.S. In 1986, Smile was a mixed success and had a short run on Broadway. The musical version of Neil Simon’s The Goodbye Girl (1993) closed after only 188 performances, although he received a Drama Desk nomination, for Outstanding Music.  Shortly before his death, Hamlisch finished scoring a musical theatre version of The Nutty Professor, based on the 1963 film. The show played in July and August 2012, at the Tennessee Performing Arts Center (TPAC) in Nashville, aiming for a Broadway run. The book is by Rupert Holmes, and the production was directed by Jerry Lewis.

Hamlisch was Musical Director and arranger of Barbra Streisand’s 1994 concert tour of the U.S. and England as well as of the television special, Barbra Streisand: The Concert, for which he received two of his Emmys. He also conducted several tours of Linda Ronstadt during this period, most notably on her successful 1996 Dedicated to the One I Love tour of arenas and stadiums.

He held the position of Principal Pops Conductor for the Pittsburgh Symphony Orchestra, the Milwaukee Symphony Orchestra, the San Diego Symphony, the Seattle Symphony, the Dallas Symphony Orchestra, Buffalo Philharmonic Orchestra, The National Symphony Orchestra Pops, The Pasadena Symphony and Pops, and the Baltimore Symphony Orchestra. At the time of his death, he was preparing to assume responsibilities as Principal Pops Conductor for The Philadelphia Orchestra.

Hamlisch was one of only twelve people to win all four major U.S. performing awards: Emmy Award, Grammy Award, the Oscar and Tony Award.[citation needed] This collection of all four is referred to as an “EGOT”. Hamlisch and Richard Rodgers are the only two people to have won this series of awards and a Pulitzer Prize.  He earned ten Golden Globe Award nominations, winning twice for Best Original Song, with “Life Is What You Make It” in 1972 and “The Way We Were” in 1974. He also received six Emmy Award nominations, winning four times, twice for music direction of Barbra Streisand specials, in 1995 and 2001. He shared the Pulitzer Prize for Drama in 1976 with Michael Bennett, James Kirkwood, Nicholas Dante, and Edward Kleban for his musical contribution to the original Broadway production of A Chorus Line.

Hamlisch received a Lifetime Achievement Award in 2009 at the World Soundtrack Awards in Ghent, Belgium. He was also inducted into the Long Island Music Hall of Fame in 2008. In 2008, he appeared as a judge in the Canadian reality series Triple Sensation which aired on the Canadian Broadcasting Corporation. The show was aimed to provide a training bursary to a talented young man or woman with the potential to be a leader in song, dance, and acting. In 2008, Hamlisch was also inducted into the American Theatre Hall of Fame.

Hamlisch’s health began to suffer and he required a kidney transplant but told his wife “he would rather die than be ahead of someone on a waiting list.” A close friend stepped in to resolve the problem and donated a kidney to him. The new kidney functioned well, but complications from an unrelated condition arose; and, four months after the transplant, he fell into a coma from which he did not awaken. Hamlisch died on August 6, 2012, in Los Angeles, California at age 68, primarily due to respiratory arrest caused by a combination of anoxic brain encephalopathy and hypertension.

The Associated Press described him as having written “some of the best-loved and most enduring songs and scores in movie history”. Streisand released a statement praising Hamlisch, stating it was “his brilliantly quick mind, his generosity and delicious sense of humor that made him a delight to be around.” Aretha Franklin called him “classic and one of a kind,” and one of the “all-time great” arrangers and producers. The head of the Pasadena Symphony and Pops commented that Hamlisch had “left a very specific … original mark on American music and added to the great American songbook with works he himself composed.”

At 8:00 p.m. EDT on August 8, the marquee lights of the 40 Broadway theaters were dimmed for one minute in tribute to Hamlisch, a posthumous honor traditionally accorded to those considered to have made significant contributions to the theater arts.  Barbra Streisand, Aretha Franklin and Liza Minnelli took turns singing songs by Hamlisch during a memorial service for the composer on September 18, 2012. At the 2013 Academy Awards, Barbra Streisand sang “The Way We Were” in Hamlisch’s memory.