Harper, who stepped in at 10 days notice – when Galina Vishnevskaya was not granted permission to leave the USSR – to sing the soprano part in the 1962 premiere of Britten’s War Requiem, has died at the age of 88. 'We none of us knew exactly what it was we had in our hands,' she recalled later. At the first performance she was aware of having her nose in the copy: ‘I felt I didn't know what it all was about till the night after.' 

Born in Belfast, Harper studied at Trinity College of Music, initially as a mezzo and then retrained as a soprano. Her first professional experience was with the George Mitchell Singers and the BBC Chorus. She made her stage debut in Verdi’s Macbeth with the Oxford University Opera Club and then joined the English Opera Group where she sang from 1956 to '75. Among her key roles were Elsa in Wagner’s Lohengrin (which she sang at Bayreuth under Rudolf Kempe – Orfeo has released a recording from the 1967 Festival), Richard Strauss’s Empress in Die Frau ohne Schatten, the Marschallin, Ariadne, Chrysothemis and Arabella, the Mozart Figaro Countess and, notably, Britten’s Ellen Orford (Peter Grimes), the Governess in The Turn of the Screw (both roles she recorded with Sir Colin Davis), Helena (A Midsummer Night’s Dream) and Mrs Coyle in Owen Wingrave ( a role she created in 1970). She sang at Covent Garden, the Met, in San Francisco and, regularly, at the Teatro Colón in Buenos Aires.

She recorded extensively: she reprised the soprano part in Britten's War Requiem for Richard Hickox and Chandos, a set that won Gramophone’s Engineering and Choral Awards in 1992. She appears on Sir Georg Solti’s classic Decca recording of Mahler’s Eighth Symphony, made in Vienna with the Chicago Symphony Orchestra, as well as the conductor's Mahler Second, on Carlo Maria Giulini’s EMI set of Beethoven’s Missa solemnis (EMI) and Otto Klemperer’s disc of Mendelssohn’s A Midsummer Night’s Dream music (also EMI). With Britten conducting, she recorded Bach’s St John Passion (in English, for Decca) and appears on two of the Vaughan Williams symphonies in André Previn’s RCA cycle. Other recordings include Barenboim’s Le nozze di Figaro, Stokowski’s Beethoven Ninth, Tippett’s King Priam (conducted by David Atherton) and his Third Symphony (with Solti, a part she sang at the premiere). 

Reviewing the Davis Peter Grimes in March 1979, Edward Greenfield wrote: ‘Opposite [Jon] Vickers, Heather Harper makes a far more intense and sympathetic figure of the widow and schoolmistress, Ellen Orford, than Claire Watson does in the Britten version  – for me the one major disappointment of that set. At every point Harper (still not quite as characterful as Joan Cross was in the original production) gives “face” to the phrases, and nothing could illustrate the contrast more sharply than the key words “We've failed” at the end of her Act 2 duet with Grimes. Where Watson sings them beautifully, first soft, then loud, Harper actually makes them the culmination of that scene, as obviously they should be.’ And of her Award-winning performance in the Hickox Britten War Requiem, Alan Blyth wrote (11/91): ‘Heather Harper has at last recorded the “role” she created – indeed it is her farewell to her many admirers as she has now retired. I heard her sing it in St Paul's not long ago and thought then that her peculiar accents, her inevitable shaping of so much of the part simply had to be preserved for posterity. Her perceptions are superior to those of both Haywood (Shaw) and Söderström (Rattle) by virtue of her longer association with the piece, and her tone shows very few signs of the advancing years . Of course, Vishnevskaya's hieratical utterance (Decca) is something unique and inimitable, but for a comprehensive understanding of what Britten wanted, Harper is hard to equal.’