Jazz singer Mark Murphy in 2011. (Photo by Jean-Pierre Leduc)

Mark Murphy, a daringly original jazz singer whose unchained improvisational style made him a cult favorite and a powerful influence on a generation of younger performers, died Oct. 22 at a retirement facility in Englewood, N.J. He was 83.

He had complications from pneumonia, said his manager, Jean-Pierre Leduc.

During a career of more than 50 years, Mr. Murphy gained a devoted following for performances that were an eclectic mix of edgy vocal fireworks and dark-of-night dramatic recitations. He reshaped familiar tunes with his rich, flexible baritone and restlessly explored new musical terrain with a bold, spontaneous flair.

He recorded more than 40 albums, appeared around the world and was nominated for six Grammy Awards. But in the view of many critics and fans, his celebrity never matched his talent.

“Murphy long ago resigned himself to the idea that he would never be a household name,” critic Will Friedwald wrote in his 2010 book, “A Biographical Guide to the Great Jazz and Pop Singers.” “Yet his is one of the most consistently prolific and rewarding careers in modern music.”

Many of Mr. Murphy’s most ardent supporters were other musicians and singers, including Ella Fitzgerald, who once called him “my equal.”

Mr. Murphy brought a freewheeling impishness to his performances, which included the music of Duke Ellington and Cole Porter, the swaying bossa nova music of Brazil and one-of-a-kind works of bebop stream-of-consciousness. He would sometimes hold a single note for 12 bars, or suddenly soar from a deep, dark-hued tone to an anguished falsetto cry.

“For new people coming to Mark’s table, he is such a potent flavor,” Kurt Elling, one of Mr. Murphy’s best-known vocal proteges, told Jazz Times magazine in 2012. “It’s a very distinct and powerful spice, and not everyone’s ready for that.”

Mr. Murphy had minor hits in 1959 with “This Could Be the Start of Something (Big)” (written by talk-show host Steve Allen) and in 1963 with a version of “Fly Me to the Moon,” previously recorded by Frank Sinatra. But just as his career seemed ready to take off, the Beatles began to dominate the charts, and the landscape of popular music was forever changed.

From 1963 to 1972 he lived in London, singing in nightclubs and working as an actor. In an interview with jazz writer Leonard Feather, Mr. Murphy described those fallow years in the distinctive beatnik lingo he used throughout his life: “It was a bad time for all the boppers. All the undergrounders had surfaced in the late ’50s and early ’60s; then we had to scatter again and wait.”

When he returned to the United States, Mr. Murphy began to record for the Muse label, making a series of albums that showed a wide range of musical interests. He recorded ballads, Brazilian music and songs associated with Nat “King” Cole. He wrote lyrics for instrumental tunes, including Oliver Nelson’s “Stolen Moments” and Freddie Hubbard’s “Red Clay,” which entered the jazz repertoire.

In 1981, he recorded perhaps his mostgroundbreaking album, “Bop for Kerouac,” in which he blended the prose of Jack Kerouac’s novel “On the Road” with musical meditations on Charlie Parker, George Shearing and the jazz sensibility. (The album is out of print.)

“I grew to see that Kerouac’s writing in books like ‘On the Road’ was very jazz-like in the cadence and rhythms he used and very naturally musical,” Mr. Murphy told the Edmonton Journal in 2007. “So I borrowed that thing. I wanted to get the rush of that contemporaneous style of writing with nerve endings.”

On the final track of “Bop for Kerouac,” Mr. Murphy recited the closing lines of “On the Road”: “The evening star must be drooping and shedding her sparkler dims on the prairie, which is just before the coming of complete night that blesses the earth, darkens all the rivers, cups the peaks and folds the final shore in, and nobody, nobody knows what’s going to happen to anybody besides the forlorn rags of growing old...”

He then sang “The Ballad of the Sad Young Men,” Fran Landesman and Tommy Wolf’s mournful ballad of dying hope and fading youth. Mr. Murphy’s performance was something of a literary tour de force, as if he were delivering a Shakespearean soliloquy in the guise of a jazz song.

“There is no one better at taking a familiar or even unfamiliar old song and turning it inside out, spilling its guts and finding the feeling underneath,” Friedwald wrote in his book. “A Biographical Guide to the Great Jazz and Pop Singers.”

“Murphy does not abstract and skewer a song merely for the sake of being different, but to get at its inner meaning. By making you think differently about a song you’ve heard before, he makes it relevant and meaningful all over again.”

Mark Howe Murphy was born March 14, 1932, in Syracuse, N.Y., and grew up in nearby Fulton. He came from a musical family, sang in church choirs and began studying piano at 7. He sang in his brother’s dance band as a teenager and modeled his early vocal style after Cole and Peggy Lee.

Mr. Murphy studied music and theater at Syracuse University, graduating in 1953. That year, Sammy Davis Jr. heard Mr. Murphy at a jam session and invited the young singer to join him onstage.

Mr. Murphy recorded his first album in 1956, appeared several times on “The Steve Allen Show” and, after moving to Los Angeles, briefly worked as a backup pianist for comedian Don Rickles.

After he came back to the United States in the 1970s, Mr. Murphy lived in San Francisco for many years before moving to rural Pennsylvania in 1998. He cultivated a sometimes eccentric appearance, dyeing his facial hair and wearing a shaggy 1980s-era wig well into his 70s.

Although he rarely spoke about his private life, Mr. Murphy had a longtime relationship with his partner, Eddie O’Sullivan, who died in 1990. Survivors include a sister.

Mr. Murphy began to receive belated recognition in the 1990s for his uncompromising approach and for a supple voice that never seemed to age. He won DownBeat magazine’s readers’ poll as best jazz vocalist in 1996, 1997, 2000 and 2001.

He led master classes, taught jazz singing for several months each year in Graz, Austria, and in time came to be recognized as one of the most innovative jazz singers of his generation. Echoes of his sound can be heard in Elling, Theo Bleckmann, Ian Shaw and many other singers.

Mr. Murphy made some of his most heartfelt albums late in his career, including “Once to Every Heart” (2005) and “Love Is What Stays” (2007). He continued to perform through 2012.

“You find out who you are from improvisation,” Mr. Murphy said in 1997, describing his music and, in a larger sense, his life. “You throw away what’s not needed and get to what’s real.”