She trained at Marquette University's College of Music in the 1920s.
During the peak of her popularity in the 1930s and '40s, she was booked in cabarets and supper clubs at least 45 weeks a year. She appeared on the cover of Life magazine in 1939, and her recordings sold in the hundreds of thousands. Revlon even introduced a Hildegarde shade of lipstick and nail polish.
She was once referred to as a "luscious, hazel-eyed Milwaukee blonde who sings the way Garbo looks".
"Hildegarde was perhaps the most famous supper-club entertainer who ever lived," the entertainer Liberace once said. "I used to absorb all the things she was doing, all the showmanship she created. It was marvelous to watch her, wearing elegant gowns, surrounded with roses and playing with white gloves on. They used to literally roll out the red carpet for her."
She never married. She was the business partner and good friend of Anna Sosenko. That relationship ended up in litigation over the control of receipts from their joint efforts.
From the 1950s through the 1970s, in addition to her cabaret performances and record albums, she appeared in a number of television specials and toured with the national company of the Stephen Sondheim musical Follies.