He was known for his outlandish dress sense, was hailed as "the face of British horse racing" for his role as betting guru for TV Racing.
The pundit was axed from Channel 4 in 2012, prompting him to launch an unsuccessful age-discrimination case.
He also achieved fame through appearances on television entertainment programmes including Celebrity Big Brother and Celebrity Wife Swap.
His appearance on television last year sparked concern following his dramatic weight loss, which he later explained had followed a serious chest infection and complications from the flu virus.
McCririck is survived by his wife of 48 years, Jenny, who he often referred to by the nickname "The Booby".
In a statement, McCririck's family confirmed he died at a London hospital on Friday and described him as an "award-winning journalist and broadcaster" and "for many years the face of British horse racing".
"His flamboyant broadcasting style from the heart of betting ring proved extremely popular with racing fans and beyond," they said.
"Despite suffering ill health in recent months, John continued to make several TV and radio appearances."
After losing his age discrimination case in 2013, McCririck said he was "devastated" and "inconsolable" and believed he would never work in broadcasting again.
An employment tribunal panel ruled that the presenter's "pantomime persona" was "unpalatable" to a wide audience and dismissed his claim against the broadcaster.
McCririck told Sky News at the time: "There are over two million people unemployed in this country, many of them want to work and, especially for older people, I have let them down."
Tributes from the world of racing poured in following the death of McCririck, who was nicknamed "Big Mac".
Legendary former jockey Sir Tony McCoy tweeted: "Very sad to hear the news of John McCririck's passing - one of the most recognisable faces from the world of horse racing and a great at promoting our sport. Our thoughts are with Jenny."
Professional jockey Nick Schofield told Sky News: "He revolutionised betting and bookmakers - he was the face of the bookmakers.
"He was globally thought of as a funny character."
Racing pundit Kevin Blake tweeted: "Very sad to hear of John McCririck's passing. A huge personality that wasn't easy to agree with, but he knew the media game and played it very well.
"Working with him on camera was a genuine thrill. Off camera, he was a gentleman. My thoughts are with Jenny and all his family."
In a post on Twitter, the Racing Post said: "Sad to report that legendary racing broadcaster John McCririck has died at the age of 79.
"McCririck was the face of Channel 4 Racing, and one of the sport's most recognisable figures. He was also an award-winning journalist for The Sporting Life."
Ascot Racecourse released a statement saying it is "deeply saddened" by the death of McCririck.
"He was an unmistakable presence in racing, and one of the most impactful broadcasters of his generation," it said.
A family spokesman said McCririck's funeral will be a private event.