Bete Mendes was born Elizabeth Mendes de Oliveira in Santos, São Paulo. She is the daughter of Osmar Pires de Oliveira, a Sub-Lieutenant of the Brazilian Air Force, and Maria Mendes de Oliveira. She acted in school plays since she was 5.

However, her artistic career really began at age 15, in her hometown of Santos, in the role of bunny Naná in the play A Árvore que Andava, by Oscar Von Phull.

Mendes has a degree in performing arts by the University of São Paulo (USP), and was pursuing a degree in Sociology when she was arrested by the political police of the military dictatorship.

She performed by the first time in theatre with the play A Cozinha (The kitchen) on 1968. At that same year, she had a prominent role in the popular TV Tupi soap opera Beto Rockfeller.