Mary Cass, who has been described as "a brilliant lawyer" who was "fit for high judicial office" , was admitted to the New South Wales Bar on 18 October 1963. Earlier resident at Sancta Sofia College while studying full-time at the University of Sydney, she had graduated with a Bachelor of Laws in 1954. After serving articles with Beswick Heydon & Lochrin, she was admitted as a solicitor on 29 July 1955. She was in practice until being called to the Bar, where she demonstrated skill in all jurisdictions but came to specialise mainly in equity, as well as landlord and tenant. It has been said that she was nicknamed 'The Winner' because of the regular victories she achieved for her clients. Right up until her death in 1992, she had chambers at Wardell.

Sources used to compile this entry: Bannon, Alexander, 'Mary Cass Memoir', in Pioneering Women at the NSW Bar: 1921-1975, Memoir Completed 2010, New South Wales Bar Association, 2011, http://archive.nswbar.asn.au/docs/about/history/oral/wbf/content/pdfs/11_mary_cass/Mary%20Cass%20memoir%20by%20Alex%20Bannon.pdf#view=fit; Brodsky, Juliette, 'Mary Cass Interview', in Pioneering Women at the NSW Bar: 1921-1975, New South Wales Bar Association, 2011, http://www.nswbar.asn.au/the-bar-association/pioneering-women/#/11_mary_cass; Brodsky, Juliette, 'Mary Cass Interview: Interview with Judge Peter Maiden SC about the late Mary Cass by Juliette Brodsky', 28 June 2010, in Pioneering Women at the NSW Bar 1921-1975, New South Wales Bar Association, http://www.nswbar.asn.au/the-bar-association/pioneering-women/#/11_mary_cass, accessed online 19 April 2016; New South Wales Law Almanac for 1956, A. H. Pettifer, Government Printer, Sydney, 1956, p. 100; New South Wales Law Almanac for 1964, V. C. N. Blight, Government Printer, Sydney, 1964, pp. 87, 89; New South Wales Law Almanac for 1993, Bloxham & Chambers Pty Ltd, Supreme Court of New South Wales, Sydney, 1993, p. 46, http://lawalmanacs.info/almanacs/nsw-law-almanac-1993.pdf, [accessed 2016-02-08].