Even before the concert took place, on May 30, 1962, it was seen as a cultural milestone in Britain, threading together the memories of devastation and the hope of unity at the height of the Cold War.

The setting was the newly built Coventry Cathedral, which had been alongside an older medieval cathedral destroyed by German bombs during World War II. To mark the occasion, England’s preeminent composer, Benjamin Britten, had written “War Requiem,” a 90-minute musical reflection on the horrors of war.

Britten had chosen three singers as principal soloists, each representing a major power during World War II: Russian-born soprano Galina Vishnevskaya, British tenor Peter Pears and German baritone Dietrich Fischer-Dieskau.

Ten days before the performance, Vishnevskaya, the wife of cellist and conductor Msitslav Rostropovich, was denied an exit visa by the Soviet Cultural Ministry. Britten then called on Heather Harper, an emerging new voice on the British operatic stage, to learn the formidable soprano part.

The event proved a musical triumph for Britten, whose “Requiem” was hailed as a masterpiece, and for Ms. Harper, who performed flawlessly and went on to a renowned career in opera and on the concert stage.

Ms. Harper, who was 88, died April 22 at her home in London. The cause was aspiration pneumonia, said her former husband, Eduardo Benarroch.

Her voice was described as “lithe” and “radiant” by critics who marveled at Ms. Harper’s versatility. She effortlessly moved from the 18th-century operas of Wolfgang Amadeus Mozart and the sacred music of Johann Sebastian Bach to the thorny 20th-century compositions of Igor Stravinsky and Alban Berg. She sang on a landmark 1966 recording of George Frideric Handel’s “Messiah” with the London Symphony Orchestra, conducted by Colin Davis.

Early in her career, Ms. Harper sang 19th-century Italian operas, and she had the ability to perform lyric soprano roles, such as Micaëla in Georges Bizet’s “Carmen.” But she also had enough heft in her voice for more-dramatic parts, and she was better known for interpreting works by German and British composers, such as Richard Strauss, Ralph Vaughan Williams and Michael Tippett.

She was featured at leading international opera houses, from Covent Garden and Glyndebourne in England to Bayreuth in Germany, the Metropolitan Opera in New York, the San Francisco Opera, Teatro Colón in Buenos Aires and La Scala in Milan.

Ms. Harper was closely identified with the music of Britten and performed his “War Requiem” hundreds of times. (Vishnevskaya appeared on a best-selling 1963 recording; Ms. Harper did not record the part until 1991.)

Ms. Harper made her debut at Britain’s Royal Opera at Covent Garden in 1962, singing the role of Helena in Britten’s “A Midsummer Night’s Dream,” and later appeared in the composer’s operas “The Turn of the Screw” and “Owen Wingrave.”

She became particularly known for her role as Ellen Orford, the principal female character in Britten’s “Peter Grimes.” She was featured in a 1979 recording of the tragic opera, conducted by Davis, which won a Grammy Award. She won a second Grammy, in 1985, for best classical vocal performance for a recording of Maurice Ravel’s “Shéhérazade.”

Ms. Harper made more than 70 recordings during her career, including Beethoven’s “Missa Solemnis” and Ninth Symphony and Gustav Mahler’s “Resurrection” Symphony (No. 2) and Symphony No. 8. She worked with numerous renowned conductors, including Georg Solti, Leopold Stokowski, Otto Klemperer, Antal Dorati, Pierre Boulez, Daniel Barenboim and André Previn, who died in February.

She had what she called “an affinity for Richard Strauss,” a late-Romantic German composer of the 19th and 20th centuries. He “suits my particular kind of voice,” Ms. Harper told Toronto’s Globe and Mail newspaper in 1978. “He’s a very sensitive composer, with a long flowing musical line and those high phrases.”

She performed his melancholy concert work “Four Last Songs, and appeared in several Strauss operas, most notably as the Marschallin in “Der Rosenkavalier.”

Beginning in 1967, Ms. Harper frequently appeared at Germany’s Bayreuth Festival, which is devoted to the operas of Wagner. She won particular acclaim for her portrayals of Elsa, the principal female role and heroine in “Lohengrin.”

Ms. Harper made her debut at New York’s Metropolitan Opera in 1977, when she appeared as the Countess Almaviva in Mozart’s “The Marriage of Figaro.”

“She radiated genuine pathos, dignity and even a touch of tragedy,” music critic Peter G. Davis wrote in the New York Times. “It was a well-rounded characterization, naturally projected and alive to all the part’s dramatic possibilities.”

Heather Mary Harper was born May 8, 1930, in Belfast. Her father was a lawyer, her mother a homemaker, and both were amateur musicians.

Ms. Harper intended to become a concert pianist and moved to London to study at the conservatory of Trinity College. She focused on piano at first and also studied violin and viola before turning her attention to singing. (A sister became a professional cellist with British orchestras; a brother was the principal French-horn player with the Royal Philharmonic.)

Ms. Harper joined singing groups and the BBC chorus before singing the title role in a 1954 British production of Giuseppe Verdi’s “Macbeth.” She later appeared in a televised production of Verdi’s “La Traviata.”

“Well, it was live in those days, you couldn’t mime it and sing it later as you can now,” she told the Globe and Mail. “I had 90 seconds to change my evening dress in the third act to my nightgown in the fourth, when I am asleep and dying.”

Her performances in “Traviata” and in Giacomo Puccini’s “La Bohème” won praise and further bookings, but Ms. Harper seldom performed Italian operas later in her career. She made her debut at the Glyndebourne Festival in Mozart’s “The Magic Flute” in 1957.

Her marriages to Leonard Buck, her onetime manager, and to Benarroch, an Argentine scientist and musicologist, ended in divorce. She had no immediate survivors.

In the 1980s, Ms. Harper began teaching at the Royal College of Music in London and other music academies. She retired from performing in 1995.

Remarkably low-key for a star soprano, Ms. Harper seldom made headlines for her temperament. She accompanied herself on piano as she rehearsed, saying, “It saves the expense of having a coach do it.”

When not traveling the world to appear in operas, she stayed quietly at home in Britain, cooking and gardening. She once said that if she could have any luxury on a desert island, it would be “wool and knitting needles.”

An earlier version of this story incorrectly described the cause of death as “aspirational pneumonia.” It was aspiration pneumonia.