Lewis was born as Sonia Phyllis Hurwitz to Ann Ritz and Abraham Hurwitz, an education professor at Yeshiva University. She had one sister. Her parents encouraged her to perform and her father, who had been named New York City's "official magician" by Mayor Fiorello H. LaGuardia during the Great Depression, taught her to perform specialized magic acts by age 13. She also received instruction in acrobatics, juggling, ice skating, baton twirling, piano, and violin. She was taught ventriloquism by John W. Cooper. She continued piano and violin at New York's High School of Music and Art, dance at the American School of Ballet, and acting with Sanford Meisner of the Neighborhood Playhouse. She attended Barnard College, but left after one year to go into show business.