Martens was Chairman of the Belgian CVP (now renamed Christen-Democratisch en Vlaams CD&V) from 1972 - 79, sitting as a Deputy in the Belgian Chamber of Representatives (federal parliament) from 1974 - 91, and serving as a Senator from 1991 - 94.
He co-founded the European People's Party (EPP) in 1976 and has been EPP President since 1992.
From 1993 he was President of the European Union of Christian Democrats (EUCD), until its merger with the EPP in 1996. Martens also negotiated with Finnish conservative politician Sauli Niinistö the merger of the European Democrat Union (EDU) into the EPP (formally concluded in 2002). The successful fusion of all center-right European organizations into the EPP - currently the largest transnational European political party with 71 member-parties from 38 countries - is widely recognized as an important achievement of his European political legacy.
From 1994 - 98, he was a Member of the European Parliament, chairing the EPP Group.
From October 2000 to November 2001 he was also the President of the Christian Democrat International (CDI).
Martens holds a doctorate in law, a degree in notarial studies, and holds baccalaureate in Thomistic philosophy of the Catholic University of Louvain. He also studied international political science at Harvard University. He has practised law at the Ghent Court of Appeal.
Among the numerous national and international distinctions, he was honoured in 1998 with the Charles V Prize for his contribution to European Union.