Beverley Martyn, a British singer poised for fame in the 1960s until a whirlwind romance with a guitarist turned into a nightmarish marriage, nearly killing her dream to make music of her own, died on April 27. She was 79.

Her death was announced by the official website of the estate of her ex-husband, John Martyn.

By the time she was 18, Ms. Martyn — then known as Beverley Kutner — was already the lead singer of a band, the Levee Breakers, which had come out with a promising single, “Babe I’m Leaving You.”

When she sang at a London party in the mid-1960s attended by Barbra Streisand, Ms. Streisand came over and said with a warm smile, “I see I have competition,” Ms. Martyn recalled in her memoir, “Sweet Honesty: The Beverley Martyn Story” (2011). Around the same time, she also met Paul Simon, and the two became an item. He invited her to meet up with him and Art Garfunkel in the United States.

She contributed vocals to the duo’s track “Fakin’ It,” released in 1968, and she performed at the Monterey Pop Festival in 1967, listed on the same bill as Otis Redding, the Who and Jimi Hendrix. She went on a drive with Peter Fonda, chatted with Janis Joplin and was followed around “constantly,” she wrote, by Phil Ochs.

Ms. Kutner and Mr. Simon broke up, but she returned to Britain in a mood of idealism. In an interview with The Coventry Standard, her hometown paper in England, she praised “the hippies’ beliefs in love and beauty” and L.S.D., which, she said, had taught her “to be my own psychiatrist.”

After returning home, her friend Jackson C. Frank took her to a gig by a young guitarist with, she wrote in her memoir, “the eyes of a Botticelli angel”: Mr. Martyn.