Poussin scholar and New York University professor of art history. Costello was raised in Brooklyn. She graduated from Erasmus Hall High School, Brooklyn, NY, and then Barnard College in 1940. She continued for graduate study at New York University's Institute of Fine Arts, writing her dissertation under Walter F. Friedländer in 1951. In 1952 joined the faculty at New York University teaching undergraduates at the Washington Square campus.