Rumiana is an Associate Professor in International Law at Gonville & Caius College at the University of Cambridge. She supervises International Law and EU Law and lectures on the International Law Tripos and the LLM courses in International Investment Law, International Human Rights Law, Global Governance, International Criminal Law and EU External Relations.

Rumiana's publications center around the communitarian norms of international law and their legal effects, which are the topic of her monograph. She is also interested in the international governance of science and new technologies in the field of biomedicine. She has published on the right to benefit from science, the international regulation of human germline editing and the anticipatory duties of States in the fields of human rights and biomedical law. Rumiana wrote an expert report for the Nuffield Council on Bioethics on the international regulation of germline editing and another one on human-rights based approaches to healthcare for the Council of Europe's Steering Committee for Human Rights in the fields of Biomedicine and Health.

Rumiana practices as an Academic Door Tenant at Thomas More Chambers where she advises States and international organisations on issues of public international law. She acts as counsel in international cases before the International Court of Justice and investment tribunals. Rumiana is a member of the Co-Ordinating Committee of the Interest Group in International Bio Law at the European Society for International Law (ESIL), as well as a member of the Steering Committee and co-theme lead on 'The Past, Present and Future of Reproduction' of Cambridge Reproduction.