She completed a Bachelor of Arts in Education and master's degree at the University of Melbourne, writing her thesis on the Wharncliffe Hours in the National Gallery of Victoria (1962).
[2] She researched the frescoes of San Giovanni a Porta Latina in Rome for her doctoral dissertation (1972) under the supervision of Charles Mitchell (1912–1995) at Bryn Mawr College, Pennsylvania.
[7] She was a Life Member of the National Gallery of Victoria and an honorary curator of its collection of Early Medieval and Renaissance Art.
Together with Vera Vines and Christopher de Hamel, Manion produced the first census of Medieval and Renaissance manuscripts in Australia (in 1984)[8] and in New Zealand (in 1989).
[18] Books and journals donated from Manion's research library form the core of the Medieval and Renaissance (Early Modern) Manuscript Studies Collection established at the Allan & Maria Myers Academic Centre, serving the communities of St Mary's College and Newman College, University of Melbourne.