His passing was confirmed Wednesday by John Elkann, grandson of Gianni Agnelli and chairman of EXOR, the investment company that controls FCA.
A surprise announcement from Fiat-Chrysler in early July 2018 revealed that Marchionne was to undergo surgery for an unspecified shoulder injury.
But it faulted him for having failed to negotiate with "an important sector of Italian workers", which it said created conflict and divisions that are still being felt.
As CEO, Marchionne has led FCA through multiple plans for profitability, which the automaker has largely delivered on, and spun off Ferrari as a successful standalone business unit.
Tributes are pouring in from automotive leaders about Sergio Marchionne's skill, creativity and determination in saving Chrysler and Fiat from near-certain financial ruin.
Born in Chieti in Italy in 1952, his family subsequently moved to Canada when Sergio was 14.
Marchionne was known for turning around the Fiat brand when he joined as CEO in June 2004.
While this was a threat made many times during the legendary Italian team's long history, somehow, coming from Marchionne, it seemed more feasible.
Retaining dual Canadian and Italian citizenship, Marchionne, who qualified as a chartered accountant and attorney, began his career with Deloitte & Touche. At the time, the company had been on the brink of bankruptcy.
Mr Marchionne was seen as the driving force behind Fiat-Chrysler's growth. Marchionne is survived by his sons Alessio and Tyler, and his longtime partner Manuella Battezzato.
Marchionne, a workaholic who often slept on a sofa aboard a plane as he traveled regularly to steer Fiat Chrysler, was a heavy smoker and espresso drinker until quitting both about a year ago.