Schull was born Rebecca Anna Wattenberg in New York City, the daughter of Rachel Gutman and real estate attorney Judah Wattenberg. She is the elder sister of Writer Ben J. Wattenberg, and aunt to Journalist Daniel Wattenberg. She was married to Gene Schull, with whom she had three children, from 1951 until his death in 2008.

Schull studied acting in the United States and in Dublin, Ireland. She may be best known as Fay Cochran, the ticket agent for a one-plane Nantucket Island airline, on the long-running 1990s NBC sitcom Wings. She played the nursemaid in the 1976 Broadway play Herzl. Schull also has appeared on such films and television shows as Roseanne, Law & Order, Law & Order: Criminal Intent, United 93, Frasier, My Life, Analyze This, Analyze That, Flannel Pajamas, and Little Children. From 1982–83, she played Twyla Ralston on One Life to Live, and appeared on various other soap operas. She appeared regularly on USA Network's drama Suits until 2012, when her character died; she has since made appearances in flashback scenes.

Schull was a regular cast member on the ABC Family series Chasing Life, which ran from 2014 to 2015.