Houllier coached the French national team between 1992 and 1993, as well as leading club sides Paris Saint-Germain and Lyon to French league titles.
In his six-year stint at the helm of Liverpool, Houllier won the FA Cup, UEFA Cup and the League Cup twice.
He decided to step down as manager of English side Aston Villa in 2011 after he suffered a dissection of the descending aorta.
While Liverpool manager, Houllier underwent 11 hours of open-heart surgery after a tear was discovered in his aortic valve, according to the Liverpool Echo.
The French Football Federation said it sends its "most sincere condolences to the family and relatives" of Houllier.
One of the players who Houllier said he was most "proud" of coaching while he was Liverpool, Jamie Carragher, paid his tributes on Twitter.
"Absolutely devastated by the news about Gerard Houllier, I was in touch with him only last month to arrange him coming to Liverpool. Loved that man to bits, he changed me as a person & as a player & got LFC back winning trophies. RIP Boss,' tweeted the former Liverpool defender, who also played for England.
Houllier began his managerial career in the 1970's before making his name as manager of Lens and PSG.
The Frenchman then became joint manager of Liverpool alongside Roy Evans n 1998.
Evans resigned just three months later, leaving Houiller to take sole charge of Liverpool, leading the club to a treble in the 2000-01 season.
After undergoing that heart surgery in 2001, Houllier later returned to the dugout and remained at Liverpool for another three years before leaving in 2004.
Transforming Liverpool into a more professional club is something Houllier is credited with during his time on Merseyside.
"I would say to the players that football is the only profession where you cannot enjoy the rewards until you retire," Houllier told the Telegraph in 2019.
"Do not go to the nightclub, buy it at the end of your career. Some players use their job to have a good time. You can do that in some professions -- have a good holiday, nights out. As a professional footballer you cannot.
"We had to convince players to change their diet and make sure they rested properly. I remember giving Jamie Carragher a list of players in England who were heavy drinkers, all past their peak at the age of 26.
"There were those who made the maximum of their career by realising that, while focusing on your job means you are not sure to succeed, if you do not you are sure to fail. The players came to understand what had to change."
After leaving Liverpool, Houllier led Lyon to two French titles. His last managerial stint came at Aston Villa before he was again admitted to hospital with chest pains.
Villa assistant manager Gary McAllister stepped in and Houllier stoo down from the role at the end of the 2010-11 season with concerns that a return to the dugout could cause further health issues.
His former assistant at Liverpool, Phil Thompson, paid his tributes on Twitter, saying: "Absolutely devastated and heartbroken at the sad news of the passing of Gerard.
"My mate, my colleague, my boss. One of the greatest moments of my life was when we come together in 1998. Just to be in his company was an absolute treat. So loyal, so passionate and extremely fierce."