FCA Chairman John Elkann: The Agnelli family scion and Marchionne's boss praised his mentor's "values of humanity, responsibility and open-mindedness", adding, "My family and I will always be grateful for what he has done".
Italian President Sergio Mattarella: "Marchionne wrote an important page in the history of Italian industry".
The charismatic executive took the helm of serially embattled automaker Fiat in 2004, and was the driving force of the acquisition of then-bankrupt Detroit automaker Chrysler, which the Italian company announced in 2009 on the heels of the financial crisis.
"We are deeply saddened by the passing of Sergio Marchionne", he said.
Marchionne was born on June 17, 1952, in Chieti, a hilltop town near the Adriatic sea in central Italy. In 2009, he organized a merger with Chrysler in the US and formed Fiat Chrysler Automobiles, becoming CEO of the new company.
Sergio Marchionne, the turnaround artist credited with saving Fiat and Chrysler.
Under Marchionne - who replaced Marco Mattiacci with Maurizio Arrivabene as team principal - Ferrari has also seen a strong increase in performance since 2014, winning multiple races and challenging for the championship in the current campaign.
Under the best of circumstances, Marchionne's pending departure presented Fiat Chrysler with a major void to fill.
In the wider world Marchionne was known for brokering the alliance between Fiat and Chrysler and turning both companies around.
Marchionne was handed an automaker that lost more than 6 billion euros ($7 billion) in 2003. At the time, the company had been on the brink of bankruptcy.
Marchionne is survived by his partner, Manuela Battezzato, his estranged wife, Orlandina and his two children, Alessio and Tyler.
What we do know so far is that Marchionne underwent surgery on his right shoulder several weeks ago and that he had confirmed business appointments for late July.