Diana-Olivia Hatneanu has been a member of the Bucharest Bar Association since 2001. Her work is focused on a variety of human rights issues, including the right to a fair trial in both criminal and civil procedures. She has successfully represented victims of human rights violations both before domestic courts and the European Court of Human Rights. Highlights of her mandate include Mocanu and others v Romania and Tatar v Romania.

Hatneanu also provides expert advice on matters related to human rights to domestic and international NGOs, as well as fellow lawyers from various jurisdictions. For example, her report on prison conditions is Romania was an important piece of evidence in Florea v Carei Court House, Satu-Mare County, Romania before the High Court of Justice of England and Wales.