The panel of judges, known as the adjudicatory chamber, received the final report from the ethics committee's investigative branch on Saturday, which called for sanctions to be levelled against both men.
A guilty verdict would almost certainly crush Uefa president Platini's hopes of succeeding Blatter at the top of world football's Zurich-based governing body.
The investigative branch did not disclose the severity of the recommended sanctions, or the evidence collected, but both Blatter and Platini have been implicated in possible criminal conduct in a separate case launched by Swiss prosecutors.
In a statement, the adjudicatory chamber said it had "opened formal adjudicatory proceedings against Joseph S. Blatter and Michel Platini based on the final reports submitted by the investigatory chamber."
The chamber "intends to come to a decision in both cases during the month of December", the statement further said.
FIFA's ethics committee provisionally suspended both men — once the two most powerful figures in world football — for 90 days in October.
Blatter, Platini and their representatives can appear before the FIFA-appointed judges to mount a defence, while investigators can also make a presentation in the process that functions like an in-house court.
Multiple sources close to the case, who requested anonymity, have said that Blatter, a Swiss national, and France's Platini could face suspensions from football of between five and seven years if found guilty.
The provisional 90-day suspensions, which expire on January 5, followed the opening of a criminal case by Switzerland's attorney general.
Swiss prosecutors said they were targeting Blatter for possible criminal mismanagement during his tenure as Fifa's president, including signing off on a dodgy TV rights deal.
Platini was questioned over a suspect $2-million payment he received from Fifa in 2011, reportedly for work done a decade earlier.
Blatter had already agreed to step down as Fifa's president following a special election in February, a concession made days after the United States charged 14 ex-Fifa officials and sports marketing executives with $150-million
worth of corruption going back decades.
Those indictments kicked off an unprecedented scandal at FIFA, sparking widespread calls for massive reforms, including from some of the world's largest corporations which sponsor the World Cup.
For Blatter, a guilty verdict would speed up his departure date from FIFA.
But for Platini, who had been the favourite to succeed Blatter, a conviction by FIFA's ethics watchdog could mark a stunning end to his career in football governance.
He remains a candidate in the presidential vote, but has been barred from campaigning during his suspension, while five other candidates who have already passed an ethics test have been free to make their case to Fifa's 209 member associations.
In excerpts of an interview given to Swiss broadcaster RTS released on Sunday, Blatter declared Platini to be an "honest man", echoing previous comments from both men that the $2-million payment was legitimate.
Blatter assured that if Platini emerges from the suspension saga, he will win the presidential vote.
Platini representatives have lashed out at the ethics review process in recent days, claiming that FIFA had lost all credibility in its handling of the ex-Juventus star's case.