Callista was admitted as a lawyer in 2012 and called to the Bar in 2023.

Before being called to the Bar, Callista practised at Freshfields Bruckhaus Deringer, in Paris, London and Singapore. She was also an associate to the Honourable Justice Susan Kiefel AC at the High Court of Australia and research associate to Professor James Crawford AC SC.

Callista accepts briefs in all areas of law. She has particular expertise in international commercial arbitration, investment arbitration and public international law. She has acted as counsel in international commercial arbitrations under a range of arbitral rules, including the UNCITRAL and ICC Rules, and in investment arbitrations, including before ICSID tribunals. Callista also has experience in proceedings before the International Court of Justice, the International Tribunal for the Law of the Sea, UNCLOS Annex VII tribunals and the European Court of Human Rights.

Callista holds a PhD in law from the University of Sydney and a Master of Law (First Class Honours) from the University of Cambridge.