Ronaldo, 35, who helped Brazil win their fifth World Cup in 2002, joined the LOC's three-man decision-making board as he followed in the footsteps of Michel Platini and Franz Beckenbauer.
Platini and Beckenbauer were head of the local organising committees when France and Germany hosted the 1998 and 2006 editions respectively.
Ronaldo took up the challenge at the request of embattled Brazilian Football Confederation (CBF) and LOC president Ricardo Teixeira who has led football in his country since 1989 and is also a member of FIFA's ruling executive committee.
"The moment for conciliation has arrived so we can stage the best and most beautiful World Cup of all time," Teixeira told a news conference on Thursday.
"Ronaldo, who the public idolise, is the perfect voice for the moment of conciliation."
Former World Footballer of the Year Ronaldo, who has noticeably put on weight since he stopped playing in February, said: "This is the ideal moment to bring together everyone who is involved in this process.
"This is not FIFA's World Cup, not the CBF's World Cup, not the government's World Cup, it belongs to the public and they have to be proud of this World Cup, they have to take part in this World Cup.
"I want to do this for the public, the public deserve my contribution," added Ronaldo.
TROUBLED PREPARATIONS
Brazil's preparations have been hit by delays in building stadiums, airports and other infrastructure and there have also been disputes between the various parties.
Congress is dragging its heels over legislation needed so that special conditions demanded by world football's ruling body FIFA can take effect.
These conditions cover issues such as ticket sales and pricing, protection of trademarks and a ban on vendors not licensed by FIFA in and around stadiums.
Some Brazilian politicians, led by former international Romario, have said the conditions are an affront to his country's sovereignty.
Teixeira is being investigated by Brazil's federal police on suspicion of corruption and money laundering.
He denies any wrongdoing but the allegations have raised questions about his suitability for organising the World Cup.
Pele, Brazil's greatest player, does not get on with Teixeira and is not involved in the LOC but he was named by President Dilma Rousseff as a special ambassador for the tournament - a move seen as a rebuff of the CBF president.
Rousseff has effectively frozen Teixeira out of negotiations with FIFA and made it clear to its executives, including general secretary Jerome Valcke, she does not have confidence in the LOC president, an official with knowledge of the talks told Reuters recently.
Ronaldo said he was putting his reputation on the line by joining the committee.
"When I asked myself why I would accept this task I concluded I had nothing to win and could only lose," he
