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.