From 2012-2020, Dennis was elected by his peers as the sole representative of the legal profession in the Hong Kong Legislative Council. Whilst in public office, Dennis focused on defending the rule of law, freedom and advancing democracy in Hong Kong. In November 2020, due to his stance on democracy and freedom, he was disqualified from office by the People’s Republic of China National People's Congress. After leaving Hong Kong, Dennis spent his time doing research and teaching at Harvard, Northeastern University, Georgetown and Tokyo University. In 2023, he co-founded the China Strategic Risks Institute, a global policy think tank. 

On the international level, Dennis continues to advocate for open society and democratic values. Dennis uses this experience to advise democratic governments, think tanks and multinational corporations on the geopolitical risks and policies related to the China and APAC region.  

Dennis practiced law with a focus in the Asia Pacific Region for 25 years. He started his legal career with the international firm Herbert Smith and went on to practice as a barrister in Hong Kong from 2006 to 2023. He advised and represented international businesses in complex litigation, arbitration and cross-border commercial transactions. 

In recognition for his work in public office, Dennis is the recipient of the New York State Bar Association Award for Distinction in International Law and Affairs 2022, and the Commonwealth Law Conference Rule of Law Award 2021. He was appointed as a Senior Fellow of Harvard Kennedy School, Ash Centre from 2021 to 2023, and as a Distinguished Scholar at Georgetown University School of Foreign Service in 2021. He taught as a visiting Associate Professor at Tokyo University, and is currently a faculty affiliate at the Center for International Affairs and World Culture at Northeastern University.