The Rio State Government said the cancellation was related to finances, while Soccerex directors said official support was withdrawn because of the fear of civil unrest.
The gathering of 4,500 delegates involved in soccer administration, marketing, sponsorship and the media, was due to be held from November 30 to December 5 at the Maracana Stadium in Rio ahead of the draw for the 2014 World Cup in Brazil.
The cancellation is a major embarrassment for the city that will host the World Cup final at the Maracana next July.
The convention was expected to attract many of soccer's heavyweights travelling to Brazil for the December 6 World Cup draw. FIFA president Sepp Blatter was among those scheduled to speak.
"It is with great disappointment that we must confirm that the final Soccerex Global Convention in Brazil will now not be taking place," Soccerex said in a statement.
"With the ongoing civil unrest, the Rio de Janeiro State Secretary of Sport took the political decision to withdraw their support from the Soccerex Global Convention."
"Preparations for the event at the Maracana Stadium were well advanced with content planned, speakers confirmed and partnerships in place."
Millions of people took to the streets of Brazil in June to protest against a rise in bus fares and a lack of investment in public services.
Some protesters armed with bricks and Molotov cocktails even tried to invade stadiums hosting Confederations Cup soccer matches as they complained about the 7.6 billion Brazilian reals (£2.06 billion) being spent on 12 World Cup venues.
The protests have spluttered on in several cities and, although much smaller, they have become increasingly violent.
However, while Soccerex CEO Duncan Revie said Brazilian officials cancelled the conference "because of the civil unrest in the country," two sources told Reuters money was an issue.
Marcelo Damato, a columnist with sports newspaper Lance!, said the Rio government, who owned and ran the Maracana until it was renovated earlier this year, told Soccerex they could hold the conference at the stadium for free.
But the consortium now running the arena wanted to charge Soccerex six million reals.
Another source familiar with the negotiations, who spoke on condition of anonymity, confirmed this was the case and a Rio state government statement also indicated money was the problem.
"The government negotiated all this without consulting the stadium management," said the source.
The Rio government confirmed the Soccerex event would not go ahead but denied the reason was civil unrest.
"The state guarantees the security of multiple events, including New Year's Eve (celebrations) on Copacabana beach, carnival, and the World Cup," it said in a statement read out by FIFA's head of media Delia Fischer at a media conference in London promoting Brazil at a global travel trade fair.
"The government of Rio de Janeiro encouraged the organisers to seek cultural and sports incentives and they failed to do so. Soccerex were advised to seek funding to host the event so that the state would not have to use public money," it added.
The Maracana stadium's owners said they had not been officially informed of the decision and declined to comment.
FIFA's marketing director Thierry Weil told reporters in London: "We are as surprised as anybody at this change of plans but we do not believe it will have any influence on the hosting of the World Cup.
"It's a pity it has been cancelled, it's never good when you cancel such an event. Flights and hotels have been booked and this causes massive disruption, but this won't impact on the World Cup," he added referring to next year's June 12 to July 13 tournament.
Carlos Cardim, head of the special advisory office on international affairs at the Brazilian embassy in London, said: "This was not an official government conference, it is a private conference. We have very few official government conferences in Rio.
"I do not know why this has happened yet but it is a shame for all those people involved."
Soccerex, established in 1995, is the leading provider of business events for the global football community.
It brings together key industry decision makers from the world of football, providing a commercial environment where delegates can benefit from business opportunities.
- Sports & Recreation