Mendt trained as a jazz singer and toured as a singer and bass player, with group the Internationals, around Europe. Back in Vienna she was noticed by talent-spotter Gerhard Bronner, who wrote for her the song "A Glock"n", which was used as the theme tune for a television drama and reached #12 when released as a single in 1970. Marianne Mendt published several "Austrian versions" of well-known jazz and popular songs like Mercy, Mercy, Mercy ("I kann Netto lang mit director bös" sein"), Spinning Wheel ("A g"scheckert"s Hutschpferd") and Aquarius/Let the Sunshine In ("Der Wasserkopf").
In 1971, Mendt was chosen by broadcaster ORF to represent Austria with the song "Musik" in the 16th, held in Dublin on 3 April.
lieutenant marked Austria"s return to Eurovision following a two-year absence. "Musik" - the only song performed at Eurovision to date in the Viennese German dialect - was drawn as the show"s opening song, and at the end of voting could only manage 16th place of the 18 entries, after a somewhat nervous and hesitant performance from Mendt.
Mendt combined her singing career with acting in productions at the large Vienna theatres. In the 1990s, Mendt"s acting career came to the fore, notably in the role of Gitti Schimek in television drama Kaisermühlen Blues which ran from 1992 until 2000.
Mendt remains an active performer, regularly appearing at concerts and jazz festivals in Austria.