Former FIFA chief Blatter and suspended UEFA boss Platini were banned from all football activity over a conflict of interest in a 2 million Swiss franc (£1.35 million) payment deal made to Platini that is also the subject of a criminal investigation in Switzerland. On Wednesday, those bans were upheld, although the suspensions were each reduced by two years.
"The Appeal Committee considered that Mr. Platini's and Mr. Blatter's activities and the services they had rendered to FIFA, UEFA and football in general over the years should deserve appropriate recognition as a mitigating factor," FIFA said.
Blatter intends to take his case to the Court of Arbitration for Sport, and Platini is expected to follow.
Blatter said in a statement through his spokesman: "I am very disappointed by the appeal committee of FIFA and I will take it to the Court of Arbitration for Sport in Lausanne."
Platini also released a statement through his legal team. "The reasons given against me are baseless, trumped up and surreal, given the facts and explanations that I gave during the hearing of the appeals board," he said. "This decision is in reality a political decision taken by the FIFA administration.
"I am the victim of a system that had only one goal: To prevent me from becoming FIFA president in order to protect certain interests that I was about to bring into question."
Platini said he would pursue all possible means to appeal, starting with CAS, and that he has asked his legal team to launch an appeal to the Lausanne-based court "without waiting."
FIFA is facing a crucial point in its nearly 112-year history as it seeks a first new president since Blatter was elected in 1998. Blatter's successor will be elected on Friday.
The appeals committee is headed by Larry Mussenden of Bermuda, who is seeking the CONCACAF presidency. That election is in May.
The six-year bans began on Oct. 8, 2015, and expire in October 2021. Blatter is 79 years old, and the confirmation of his suspension likely ends his hopes of returning to football unless CAS rules in his favour.
Platini would be eligible to return in time for the Qatar 2022 World Cup that he championed.
Evidence available for the case could not show that Blatter and Platini violated Article 21 of the FIFA Code of Ethics (bribery and corruption), the FIFA statement said.
The appeal lodged by the investigatory chamber for a lifetime ban from all football-related activity was also dismissed.
Platini's provisional suspension by the ethics committee last October, pending a full investigation, stalled his presidential bid, and the ban in December effectively ended it.
Both were fined by the ethics judges in December. Blatter was ordered to pay 50,000 Swiss francs (£36,000), and Platini was fined 80,000 Swiss francs (£58,000). Both sums are now due within 30 days.
Blatter and Platini both deny wrongdoing.
They claimed the £1.35m payment was made after a verbal agreement between the pair when the Frenchman worked for Blatter from 1998 to 2002, though it was not paid until 2011, 13 years after the agreement.
The ethics committee rejected the agreement as "not convincing" in December, although it added that the evidence had not been sufficient to secure corruption charges. The appeals committee agreed with that assertion.
The charges proven in December included offering and accepting gifts, conflict of interest and violating fiduciary duty to FIFA.
The appeals committee reduced the five-year ban for a breach of Article 20 (offering and accepting gifts and other benefits) by one year and reduced three-year bans for other violations.
The appeal verdicts come two days before 207 of FIFA's member associations -- Kuwait and Indonesia are suspended -- vote in the election. Platini had hoped to be in contention for the post.
Jordan's Prince Ali Bin Al Hussein, Sheikh Salman Bin Ebrahim Al Khalifa of Bahrain, UEFA general secretary Gianni Infantino, South Africa's Tokyo Sexwale and Jerome Champagne, a former FIFA deputy secretary general from France, are all vying for the top job.
FIFA is also expected to approve wide reforms to guard against corruption this week. The reforms will be voted on ahead of the presidential election.
The adjudicatory chamber of FIFA's independent ethics committee earlier on Wednesday opened formal proceedings against former CONMEBOL vice-presidents Luis Bedoya and Sergio Jadue.
FIFA's ethics committee earlier this month recommended lifetime bans from football for the pair, who each pleaded guilty to charges of racketeering conspiracy and wire fraud conspiracy in December, having been indicted as part of the long-running criminal investigation into corruption within FIFA.