The Frenchman said he would resign to pursue the case over a suspect $2 million payment in Swiss courts in a bid to clear his name.
The Court of Arbitration for Sport rejected the appeal saying it was not convinced about the “legitimacy” of the payment ordered by ex-FIFA president Sepp Blatter.
It did cut the ban to four years and reduced a fine from 80,000 Swiss francs ($80,000) to 60,000 Swiss francs.
“I note today’s decision by the Court of Arbitration for Sport but I consider it a profound injustice,” Platini said in a statement.
“This decision inflicts a suspension for which the length stops me, de facto, and by luck, from being a candidate in the next FIFA presidential election,” he added.
“As agreed with the national associations, I resign as president of UEFA to pursue my fight before the Swiss courts to prove my probity in this case.
“Life has always kept beautiful surprises for me, now I am free to live them,” said the former French football star.
The decision means that Platini will not be able to take any official role in the European Championship finals that start in France on June 10. He was a key organiser of the event until the FIFA payment scandal erupted.