Born in Vienna, she studied in Italy; among her teachers were Aloysia Weber Lange and Domenico Ronconi. Her stage debut, in her native city, came in 1821, when she performed in Mozart's Così fan tutte, a performance for which Franz Schubert had briefly served as her répétiteur. Three years later she sang in the first performances of Ludwig van Beethoven's Ninth Symphony and Missa Solemnis.
She performed a great deal in Italy, principally in Naples after 1825 when she became engaged to the impresario of the Teatro San Carlo, Domenico Barbaia. Among the roles written for her were those of Isoletta in Vincenzo Bellini's La straniera (1829, Milan), Gaetano Donizetti's Parisina (1833, Florence), Antonina in Belisario (1836, Venice), Maria de Rudenz (1838, Venice), and Bianca in Saverio Mercadante's Le due illustre rivali (1838, Venice).
Unger had a great success at the Théâtre-Italien in Paris in October 1833, where Sadie speculates that this was the occasion upon which Rossini is known to have commented on her voice as having "the ardour of of the south, the energy of the north, brazen lungs, a silver voice and a golden talent".
In 1841 she married the French writer François Sabatier and retired from the stage in 1843.
She is memorable for her part in the famous anecdote regarding the applause at the premiere of Beethoven's Ninth Symphony – it was reportedly she who turned the completely deaf composer around to receive his audience's thunderous applause.
- Sadie 1998, p. 867
- Rossini, quoted in Sadie 1998, p. 867
- Ewen, David (1955), Encyclopedia of the Opera, A. A. Wyn, Inc.
- Sadie, Stanley, (Ed.) (1998), "Unger, Karoline" in The New Grove Dictionary of Opera, Vol. Four, p. 867. London: MacMillan Publishers, Inc. ISBN 0-333-73432-7 ISBN 1-56159-228-5