The CAS ruled that the penalty initially imposed by FIFA's ethics committee was "too severe".
But it also stated it was "not convinced" that the 1.8 million euros payment Platini received from FIFA in 2011 was legitimate.
CAS said the punishment of the French football legend was "justified in view of the superior functions carried out by Mr. Platini, as well as “the absence of any repentance and the impact that this matter has had on FIFA's reputation".
Indeed, when Platini walked out of the courthouse on Monday he said that he had done nothing wrong.
“It is like you’re in front of the goal,” he said about the hearing. “You have to be precise, clear and concise. So I have worked and made a bill, according to the regulations of the FIFA. I got the money, I paid the taxes, and that’s it.”
The 1.8 Euro payment was ordered by FIFA’s ex-president Sepp Blatter, who was also brought down over the transaction.
Blatter is under criminal investigation in Switzerland over the transaction and other aspects of his management of FIFA.
The pair are the highest-profile casualties in a set of corruption scandals within world football, which has seen dozens of long-serving FIFA executives arrested and charged with corruption.
Meanwhile, Michael van Praag, head of the Dutch football association KNVB and a possible contender to replace Platini, declined to comment on the ruling but called on Europe "to show unity".
The ruling means Platini will be barred from presiding over the Euro 2016 that opens in France on June 10, a tournament which he helped organize until he was provisionally suspended by FIFA in December.