The lifelong heavy smoker died yesterday in a Warsaw hospital following a long illness, close friend and Senate speaker Bogdan Boruzewicz confirmed.
A Catholic intellectual who dedicated his life to fighting totalitarianism, Mazowiecki was "one of the fathers of Polish liberty and independence", Foreign Minister Radoslaw Sikorski told Polish Radio.
One of the early members of the Solidarity movement, he became prime minister in August 1989, two months after Solidarity won elections and its iconic leader Lech Walesa tapped him for the job.
"Mazowiecki was the best prime minister Poland ever had," the Nobel peace laureate said.
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European Parliament President Martin Schulz called Mazowiecki a "noble character" who had been "instrumental in changing the history of Poland and Europe."
US State Department spokeswoman Jen Psaki said Mazowiecki was leaving "behind an important legacy.
"He worked to improve relations with the West, paving the way for Poland's eventual accession to NATO and the European Union."
A false rumour about Mazowiecki's death in detention during the December 1981 Communist party Martial Law crackdown on Solidarity earned him obituaries in the international press and a funeral mass in Paris.
In the mid-1990s, Mazowiecki served as a special UN envoy for ex-Yugoslavia, but quit the post after the Srebrenica massacre of some 8,000 Muslim boys and men by Bosnian Serb forces in July 1995.
A lawyer by training, he was born in the central town of Plock on April 18, 1927.
As the anti-communist Solidarity movement swept Poland in 1980, Mazowiecki was among the first intellectuals to join striking workers at the Gdansk Shipyard where he first encountered union leader Walesa.
Mazowiecki's funeral will be held on Sunday, the government announced last evening.