Mr Vlassis holds a law degree from the University of Athens (Greece) and an LLM (Master of Laws) from the University of Miami (USA). He has pursued post-graduate studies in international law at the George Washington University. He is licensed to practice law in Greece and is a member of the Athens Bar Association.

Mr Vlassis was recruited by the United Nations in 1989 following the successful completion of the United Nations National Competitive Examination, and has been working with the United Nations Office on Drugs and Crime (UNODC) ever since.

He was Secretary of the Ad Hoc Committee for the Elaboration of the United Nations Convention against Transnational Organized Crime from 1998 to 2003, and the Secretary of the Conference of the Parties to that Convention from 2004 to 2008.

From 2001 to 2003, he was Secretary of the Ad Hoc Committee on the Negotiation of a Convention against Corruption. Currently, he is Secretary of the Conference of the States Parties to that Convention.

As Chief of the Corruption and Economic Crime Branch, he leads UNODC's work on action against corruption and other forms of economic crime.

Mr Vlassis is married with two children.