The 60-year-old, sanctioned over a $2 million payment he received from FIFA, saw CAS -- sport's final court of appeal -- cut his ban to four years, but it's a ruling that effectively leaves Platini in limbo.
He is unable to engage in any football-related activity at national or international level, although CAS did cut a FIFA fine imposed on Platini from $82,500 to $62,000.
"I accept today's decision by the Court of Arbitration for Sport but I consider it a profound injustice," said Platini in a statement.
"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."
CAS said that its arbitrators were of "the opinion that a severe sanction could be justified in view of the superior functions carried out by Mr. Platini (FIFA vice president and UEFA president), the absence of any repentance and the impact that this matter has had on FIFA's reputation."
In December 2015, Platini and former FIFA president Sepp Blatter were each banned for eight years after the FIFA Ethics Committee found that the former had received a two million Swiss franc ($2.02 million) "advisory payment."
The committee found that both had broken the FIFA Code of Ethics
with regards to conflicts of interest, breach of loyalty and gifts. The pair were cleared of bribery and corruption allegations.
In February, FIFA
denied appeals from Blatter and his one-time heir apparent Platini to strike down their bans from "all football-related activities."
But FIFA did reduce both men's bans from eight to six years, citing their service to football as justification for the decision.
The contract between Platini and Blatter, signed in 1999, ended in 2002 when the Frenchman became a member of FIFA's executive committee.
"It was not until 1 February 2011 -- four months prior to the FIFA presidential elections and at a moment when Sepp Blatter and Mohamed Bin Hammam were both still candidates to the election that FIFA paid the amount of CHF 2'000'000 in favour of Mr. Platini," said a CAS statement.
"Mr. Platini justified such payment as back pay, explaining that he had orally agreed with Mr. Blatter in 1998 when the future FIFA President was negotiating with him, to an annual salary of CHF 1'000'000.
"The Panel, however, was not convinced by the legitimacy of the CHF 2,000,000 payment, which was only recognized by Mr. Platini and Mr. Blatter, and which occurred more than eight years after the end of his work relations."
UEFA's Executive Committee will meet in Basel on May 18 to schedule an elective congress to appoint Platini's successor, though European football's governing body has no plans to make an interim appointment.