Roberta Flack’s pensive version of Bridge Over Troubled Water, from her 1971 album Quiet Fire, so impressed another rising star that he sent her a fan letter. “Dear Roberta,” wrote Elton John, “I have never heard anything this beautiful in years ... ”

Flack, who has died aged 88, must have seemed both familiar and fascinatingly different to the young English songwriter. Like John, she was a classically trained pianist who had gravitated to pop. But she was North Carolina born, and had taught in high school before having her first hit at the age of 34. Her career was founded on her ability to sell a song using reticence and reserve, qualities that defined her from the early smash singles, The First Time Ever I Saw Your Face and Killing Me Softly With His Song, to her final album, a collection of Beatles covers released in 2012.

Hit-making partnerships with the singers Donny Hathaway and Peabo Bryson stayed in the same nuanced lane, with few departures into drama or melisma. Even as R&B became more experimental in the 1970s and 80s, Flack burrowed deeper into a gentle musical conservatism. Bar the occasional flash of social consciousness, she was, in both artistry and manner, quiet when quiet was unfashionable.

Her reward was a string of chart hits, four Grammy awards and the loyalty of America’s adult-contemporary radio stations. Her success on AC radio also opened up the white-leaning, soft-pop format to other African-American artists.

Flack sang as if romance were a subject deserving deep, measured consideration – a style that complemented her voice. Clarity and perfect pitch were her distinguishing vocal features, developed in part by spending her adolescence listening to the soprano Leontyne Price. If her love of opera did not set her apart enough from other teens in Arlington, Virginia, where she grew up, she was also a piano prodigy, winning a music scholarship to Howard University in Washington DC when she was 15.

Though influenced by jazz, R&B and easy listening, Flack was not quite any of them – in the NME’s spot-on description, she created a middle ground between “genteel promiscuity and stronger codes of heartbreak – always with the lamps down low”.

Her early albums were partly informed by the turbulence of the civil rights era – the 1969 track Tryin’ Times was unabashed protest soul – but by primarily sticking to apolitical timelessness, she became one of the top female singers of the 70s, in any genre.

Some critics unfavourably compared her to more visceral contemporaries such as Aretha Franklin, which provoked the retort: “I am a black person who sings the way I do. I am not a black person who sounds anything like Aretha Franklin or like Chaka Khan. I shouldn’t have to change in order to be who I am.”

The comparisons were unfair, anyway: Franklin’s style had been forged in the Baptist church, whereas Flack had grown up as a restrained, hymn-singing Methodist. That was especially evident in sporadic nods to her southern church background, such as the bawdy 1970 single Reverend Lee; she could be muscular when required, but never to the point of full, bodily immersion.

The thoughtful approach served her well. The First Time Ever I Saw Your Face was the US’s top-selling single of 1972 and won record of the year at the 1973 Grammy awards. At the 1974 Grammys, Killing Me Softly – a five-week US No 1 – took record of the year and female pop vocal performance.

She was born in Asheville, North Carolina, one of four children of Laron Flack, a tobacco picker, and Irene Council, a school cook. The family moved to Virginia when Roberta was five, by which point she was already playing the piano. Practising on an upright her father rescued from the local dump, by the age of 13 she was proficient enough to come second in a statewide contest for black students.

She was bright, finishing high school early and graduating from university at 19 with a degree in music education. For the next seven years she taught in the Washington school system, while developing a sideline as a pianist/singer in local bars. In 1968 she was spotted by the jazz pianist Les McCann, who was so taken by her voice – “I laughed, cried and screamed for more,” he said – that he introduced her to Atlantic Records.

Flack’s jazzish, folkish early albums made a muted impact. Arguably, she owed her eventual success to the fact that Clint Eastwood paid her $2,000 in 1971 to use The First Time Ever I Saw Your Face in the film he was then directing, Play Misty for Me. The song, from her 1969 debut First Take, had not previously been a single, but was released when it proved one of the film’s talking points.

It duly spent six weeks at No 1, establishing Flack as a major artist. Her grip on the mid-70s charts was strengthened by duets with Hathaway – in particular, The Closer I Get to You and the Grammy-winning Where Is the Love, which were among the best songs either artist ever made.

In the early 80s, when the hits had dried up, a series of duets with Bryson, notably Tonight I Celebrate My Love, brought her back to the charts. Her last big seller was a synth-soul double act with Maxi Priest, Set the Night to Music, which reached the US Top 10 in 1991.

In the years that followed, Flack took the fail-safe route of many veteran vocalists, making Christmas albums and collections of pop and jazz standards. The hip-swinging 1994 covers album Roberta received a Grammy nomination, but a likable and inventive Beatles collection, Let It Be Roberta, sank – despite the endorsement of Yoko Ono, who was Flack’s across-the-hall neighbour in the Dakota apartments in New York.

She hosted a syndicated weekly music and chat radio show between 1995 and 1998, but was more fulfilled by making music than talking about it. The Fugees’ highly successful 1996 cover of Killing Me Softly spurred Flack to release a remixed version of her 1972 hit, which duly topped the US dance chart.

After suffering a stroke in 2016, she returned to recording in 2018 with the song Running, heard in the film 3100: Run and Become, a documentary about a 3,100-mile run held annually around the streets of New York. But in 2022 it was announced that Flack had been diagnosed with ALS, amyotrophic lateral sclerosis, known in the UK as motor neurone disease, which had made it impossible for her to sing.

In 1966 Flack married the bassist Steven Novosel; this and a second marriage ended in divorce.

• Roberta Cleopatra Flack, singer, born 10 February 1937; died 24 February 2025