The former France captain, in a speech earlier on Tuesday, also promised to make international football a priority and to keep the Champions League open to clubs from the smaller of Europe's 53 associations.
The Frenchman, who has been in charge of European football's governing body since 2007, was voted in at the UEFA Congress, where he was given a standing ovation.
The 55-year-old former Nancy, Saint Etienne and Juventus player, the only candidate to register before the deadline on December 16, was visibly moved by the reception.
"I thought I was old enough not to get so emotional," he said. "Thank you from the bottom of my heart for your confidence in me."
He also thanked "the thousands of grassroots coaches and volunteers all over Europe who devote themselves out of passion and their love of football."
"They impart values to our children and grandchildren, guide them through the most wonderful school of life and help, in their way, to make our society a little better," he said.
Platini has pledged to implement his so-called Financial Fair Play policy which is aimed at making clubs live within their means.
Those who do not comply could be barred from European competition from 2014/15.
"Financial fair play is a crucial project that will enable us to clean up certain practices within our game," said Platini, who also sits on FIFA's executive committee, at the start of the Congress.
"There is a huge amount of money in football, but more importantly there is a moral problem in the way this money is sometimes generated and used."
Karl-Heinz Rummenigge, president of the European Clubs Association which represents 197 of the region's biggest clubs, welcomed the re-election of his former rival.
"During his first term of office, President Platini has set a clear vision for the future of European football," said the former West Germany forward in a statement.
"In particular, we are very pleased with the support and understanding he has shown towards European club football.
"We feel privileged to have such a supportive partner and we look forward to a continued excellent collaboration in the future."
France Football Federation president Frederic Thiriez said: "Michel Platini's triumphal re-election is a chance for European football to confront wider issues.
"It also brings pride to French football. Michel gives all his energy to defend certain values and fight against excess."
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