Delors had a high-profile political career in France, where he also served as finance minister under Francois Mitterrand.
The French socialist and ardent advocate of post-war European integration died in his sleep at his Paris home on Wednesday, his family said.
Delors served as president of the European Commission for three terms – longer than any other holder of the office – from January 1985 until the end of 1994.
During Delors’s decade as the European Commission chief, the EU completed its integrated single market and agreed to introduce a single currency, the euro, and built a common foreign and security policy.
The then-12-nation bloc also set the conditions on his watch for eventually admitting the former communist states of Central and Eastern Europe after the fall of the Berlin Wall in 1989.
Delors also served as finance minister under French President Francois Mitterrand from 1981 to 1984.
But he declined to run for the presidency in 1995 despite being overwhelmingly ahead in the polls, a decision he put down to “a desire for independence that was too great”.
“I have no regrets,” he said about that decision later. “But I am not saying I was right.”
The current French President Emmanuel Macron paid tribute to the former EU leader as an “inexhaustible architect of our Europe” and a fighter for human justice.
Posting on X, formerly Twitter, Macron said “his commitment, his ideal and his rectitude will always inspire us”. He called Delors “a statesman with a French destiny”.
Michel Barnier, the EU’s chief negotiator during the United Kingdom’s departure from the bloc, called Delors an inspiration and a reason to “believe in a ‘certain idea’ of politics, of France, and of Europe”.
Delors’s time as the European Commission president was marked by clashes between federalists such as himself who believed in an “ever closer union”, and the UK’s then-Prime Minister Margaret Thatcher, who firmly resisted any shift of power to Brussels.
“Up Yours Delors”, read a famous 1990 front-page headline in The Sun newspaper which voiced its concerns about a single currency and increased powers for the European Parliament.
Despite these challenges, he helped establish major tenets of the bloc’s integration, including the Schengen accords for travel and the Erasmus programme for student exchanges.
He is survived by his daughter Martine Aubry, a French politician and mayor of Lille, who campaigned to be the socialist candidate for the French presidency in 2011, losing to Francois Hollande.