Soprano Johanni van Oostrum was born in South Africa and studied at the University of Pretoria. She received her vocal training with Dr Mimi Coertse and was a member of the Black Tie Opera Studio. She is considered a sought-after interpreter of the great soprano roles of Strauss, Mozart, Janáček and Wagner. She recently jumped in as Elsa (Lohengrin) at the Bavarian State Opera and won over audiences and critics alike. She has also appeared as Agathe in Weber's Freischütz at Aix-en-Provence, the BOZAR in Brussels, the Theater an der Wien, the Théâtre des Champs-Élysèes in Paris and the Barbican Centre in London,  sang the title role in Richard Strauss' Salome at the Graz Opera, the roles of Marietta in Korngold's Die tote Stadt at the Opéra de Limoges and the Countess Almaviva at the Bavarian State Opera. 

She has worked with conductors such as Sir Simon Rattle, Alan Gilbert, Ivor Bolton, Yannick Nézet-Séguin, Adam Fischer, Antonello Manacorda, Oksana Lyniv, Bertrand de Billy or Laurence Equilbey as well as with directors such as Harry Kupfer, Barrie Kosky, Tobias Kratzer or Vera Nemirova.

One of her leading roles is undoubtedly the Feldmarschallin (Der Rosenkavalier), which she has interpreted under Sir Simon Rattle at the Nederlandse Opera in Amsterdam, at the Royal Swedish Opera under the baton of Alan Gilbert, at the Komische Oper Berlin or at the Bolshoi Theatre in Moscow. 

In the 20-21 season she made her debut as Leonore in a concert performance of Beethoven's Fidelio conducted by Adam Fischer and her role debut in the title role of Janáček's Jenůfa at the Konzert Theater Bern. She was Agathe in "The Freischütz Project", released on CD and DVD by Warner Classics and Erato respectively. Planned - and prevented by the pandemic - events included her house debut at the Liceu Theatre in Barcelona as Elisabeth in Wagner's Tannhäuser, her debut with the NDR Elbphilharmonie Orchestra in Hamburg with Janáček's Glagolitic Mass, a new production of Le nozze di Figaro at the Canadian Opera Company, Mahler's 8th Symphony with the Orchestre de Paris conducted by Daniel Harding, Beethoven's concert aria "Ah! Perfido" with the Insula Orchestra in Aix-en-Provence, Chrysothemis in Elektra by Strauss and Ellen Orford in Britten's Peter Grimes in Wiesbaden. 

On the concert stage, Johanni van Oostrum can be heard performing Beethoven's 9th Symphony and Missa solemnis, Four Last Songs and other orchestral songs by Richard Strauss, the German Requiem by Johannes Brahms, Mendelssohn's Elijah and Verdi's Messa di Requiem. A special concern of hers is the performance of songs by South African composers.