As a leader of a small nation of 10 million, he worked for more European integration among nations based on consensus politics. Martens "made a lasting mark on Europe and beyond," EPP chairman Joseph Daul said.
EU Commission President Jose Manuel Barroso said "his personal efforts to integrate parties from the newest democracies in Central and Eastern Europe."
Other political leaders also paid tribute to him on Thursday.
The president of the European parliament, Martin Schulz, called him "a great statesman of Belgium, Europe and an outstanding leader in the European Parliament."
EU President Herman Van Rompuy, also a Dutch-speaking Belgian Christian Democrat, remembered how Martens imposed austerity measures to counter runaway spending in Belgium during the 1980s to turn the nation around. "He lifted our country out of a morass," he said.
As much as for his political ambition, he was also renowned for a stormy amorous life, which included three marriages and five children.
A state funeral is set for Oct. 19.