Steppat appeared regularly on the German stage, and starred in more than forty movies.

In the 1960s, she appeared frequently in crime movies based on the work of author Edgar Wallace, such as Die Gruft mit dem Rätselschloss, Der unheimliche Mönch and Die blaue Hand, which brought her great fame in Germany.

In her only English-language role, Steppat played Blofeld's assistant and henchwoman Irma Bunt in the James Bond movie On Her Majesty's Secret Service.

In the first English-language conversation between Steppat and the movie's producer, Albert R. Broccoli, she confused the word verlobt (engaged) with engagiert (involved).

Steppat was unable to capitalise on her new fame outside Germany, as she died of a heart attack only four days after the movie's international release.