Tomenko began his professional career in 1992 at the Institute of National Operation and Self-government as the Head of the Political Science Department. Between 1992-1998 he was the vice-president of the Foundation "The Ukrainian Outlook", the director of the Institute of Post-communism Society and the Institute of Politics (listed are non-governmental politics research organizations). At the same time he continued lecturing history and political science courses at Kyiv universities, finally becoming the Head of the Politology department in the National University "Kyiv-Mohyla Academy".