She studied recorder in Vienna, theater at the Mozarteum in Salzburg and voice with Hertha Töpper at the Conservatory of Munich.
Von Magnus appeared at the Salzburg Festival first in 1993 in Mozart's Great Mass in C minor as well as in L'incoronazione di Poppea and Vespro della Beata Vergine 1610 of Monteverdi.
She took part in several projects with Nikolaus Harnoncourt, such as a production of Mozart's Le nozze di Figaro staged by Jürgen Flimm in Amsterdam.
Her US debut in 1991 was in Bach’s St Matthew Passion with the Los Angeles Philharmonic conducted by Peter Schreier.
Her recordings include participation in the complete vocal works of Johann Sebastian Bach with Ton Koopman and the Amsterdam Baroque Orchestra & Choir.