Seal shot to fame as Gladys in the West End transfer of The Pajama Game by Richard Adler and Jerry Ross at the London Coliseum. She then took over the role of Lola in Damn Yankees from Belita at the same theatre. This was then followed by the title role in Irma La Douce; Seal was in the lead in both the West End and Broadway productions. She won the 1961 Tony Award for Best Actress in a Musical. She later took the role of Roxie Hart in Chicago: A Musical Vaudeville (known today as Chicago The Musical) in the original London production, alongside Jenny Logan (who played Velma Kelly) in 1979.
She has been married to photographer/former actor Michael Ward (aka Theo Ward) since 1976 and is stepmother to his two daughters Sam Ward and Tasha Ward. She has three children from her former marriage to Zack Matalon. They are Adam Matalon, a film-maker based in Los Angeles, Sarah Matalon, and Noah Matalon.