Maria Grazia Morgana Messina was born on June 4, 1930, in Pleasantville, New York, to parents from Fiumefreddo di Sicilia, near Catania in Sicily. She grew up in New York City with five siblings. Her father, who ran a coal and ice business and played piano and guitar by ear, died while she was young, and the family went through a lean period afterward. A scholarship took her to the Manhattan School of Music, and she began singing professionally at sixteen as Morgana King, working Greenwich Village rooms and other New York clubs. In 1953 a record executive heard her at a Village nightclub and took an interest in her phrasing and wide range, which led to her first album three years later.

At seventeen she married the trumpeter Tony Fruscella; the couple had a daughter, and they were regular Sunday dinner guests of Charlie Parker and his family before the marriage ended in divorce in 1956. Her debut, For You, For Me, For Evermore, came out on EmArcy in 1956 with Hank Jones among the credited players, and a second Mercury album, Sings the Blues, followed in 1957. She sang at the Easter Jazz Festival at New York's Town Hall in March 1956, opened Trude Heller's in July 1957, and took part in the all-women Jazz Female concert at Carnegie Recital Hall that November. She was included in the 1960 edition of Leonard Feather's Encyclopedia of Jazz, where she said she wanted to become a dramatic actress.

Her second husband, whom she married in 1961, was the trombonist Willie Dennis, a veteran of bands led by Gerry Mulligan, Benny Goodman, Woody Herman and Buddy Rich who had also recorded for Charles Mingus's Debut label. She traveled to Brazil with him in 1960 when he toured with Rich, and the bossa nova she heard there became part of her repertoire. The new Mainstream label signed her, and With a Taste of Honey (1964), with its title song "A Taste of Honey," became her best-known record; credits on a later CD reissue place Clark Terry, Joe Wilder, Phil Woods, Hank Jones and Dennis himself on the sessions. Torrie Zito arranged the follow-up, Miss Morgana King (1965), and she appeared on The Andy Williams Show and The Hollywood Palace in 1964. She was nominated for the Best New Artist Grammy, the award that went to the Beatles.

Dennis was killed in a car accident in Central Park in 1965. Frank Sinatra offered her a deal with his Reprise label, and she made three albums there with Zito and Don Costa: It's a Quiet Thing, a memorial to Dennis, Wild Is Love (1966) and Gemini Changes (1967). Her 1967 single "I Have Loved Me a Man" reached the American easy-listening survey and the Australian Top 20. She moved to Malibu, California, and lived there for more than twenty years. A Verve album, I Know How It Feels to Be Lonely, followed in 1968.

The part that made her famous to a wider public was acting. In 1972 she played Carmela Corleone, Don Vito Corleone's wife, in Francis Ford Coppola's The Godfather, singing "Luna mezzo mare" in the wedding scene, and she returned to the role in The Godfather Part II (1974) and the television miniseries The Godfather Saga (1977). Later film parts were small: Nunzio (1978), A Time to Remember (1987) and, in 1997, her last, A Brooklyn State of Mind. Singing continued alongside. New Beginnings (1973, Paramount) was a pop-leaning set arranged in part by Bob James with Idris Muhammad on drums, and James Gavin reported in JazzTimes that Stevie Wonder praised her version of "You Are the Sunshine of My Life." From 1978 she recorded a long series for Muse, including the small-group Stretchin' Out (1978), Portraits (1984), Simply Eloquent (1986) with Ted Nash and Adam Nussbaum, and a 1987 Japanese album, Stardust, with Billy Taylor and Phil Woods. She performed at the Billie Holiday tribute at the Hollywood Bowl in July 1979, announced her retirement from live work at the Cotton Club in Chicago on December 10, 1993, and still performed occasionally afterward. Her last Muse albums came in the 1990s.

Morgana King passed away of non-Hodgkin lymphoma on March 22, 2018, in Palm Springs, California, at age 87. Her death was not publicly reported until August 2018.

King sang with a four-octave contralto and a phrasing that listeners found either spellbinding or mannered; Wikipedia notes that she had detractors, and the jazz writer Marc Myers has called her approach belabored while still praising For You, For Me, For Evermore. Gavin wrote that her improvisations drew on opera and Sephardic music as well as bop, that she preferred to rework a familiar melody from its first phrase, and that she swung hard with a very soft touch, a comparison he made to Peggy Lee. Myers heard a deep influence from Sarah Vaughan, and it has been theorized that her ornamented line owes something to a synagogue cantor she heard as a child. Gavin counted Antonio Carlos Jobim, Duke Ellington and Stevie Wonder among her admirers, and she was one of the first American singers to take up bossa nova. Her record catalog moves between jazz and pop: the standards, ballads and blues of the EmArcy, Mercury and Muse dates sit beside Beatles and Stevie Wonder songs on her Verve and Paramount albums, and many listeners know her first as an actress. Her jazz credentials rest on the club and concert work, the recording sessions with jazz players, her two marriages to jazz musicians, and her place in Feather's encyclopedia.