Born Susan Plaksin in Buffalo, New York, she was raised in Kingston, Pennsylvania, and attended Northwestern University.

[citation needed] Plakson began her career on the stage, and played four characters opposite Anthony Newley in the national revival tour of Stop the World, I Want to Get Off.

She also played Marquise Theresa Du Parc in the Broadway production of La Bête.

Plakson was a regular in the sitcom Love & War, as sportswriter Mary Margaret "Meg" Tynan.

[2][3] Plakson played the blue brontosaurus real estate agent Monica de Vertebrae on Dinosaurs, as well as many other guest voices.