Lewis, though not the first pianist in that style, was a pioneer of Piano rock, not only through his sound but also through his dynamic performance. He would often kick the piano bench out of the way to play standing, rake his hands up and down the keyboard for dramatic accent, and even sit down on the instrument. His frenetic performance style can be seen in films such as High School Confidential (he sang the title song from the back of a flatbed truck), and Jamboree. He has been called "rock & roll's first great wild man and also rock & roll's first great eclectic." These performance techniques have been adopted by later Piano rock artists, notably admirers Elton John, Billy Joel, and Ben Folds.

He married Jane Mitcham, his second wife, 23 days before his divorce from his first wife was final.

Lewis' turbulent personal life was hidden from the public until a 1958 British tour, when reporters learned about the twenty-three year old star's third wife Myra Gale Brown. She was thirteen years old, and Lewis's first cousin once removed. The publicity caused an uproar and the tour was cancelled after only three concerts.