The 23-year-old has been suspended for the rest of the regular season and the playoffs. He must meet with NFL Commissioner Roger Goodell before any possible reinstatement.
Pittsburgh offensive lineman Maurkice Pouncey was also suspended for three games while Cleveland defensive lineman Larry Ogunjobi was suspended for one game.
Both the Steelers and Browns were fined $NZD366,000 and all three players were fined an undisclosed amount.
'I MADE A TERRIBLE MISTAKE'
"Last night, I made a terrible mistake," Garrett said in a statement released by the Browns. "I lost my cool and what I did was selfish and unacceptable.
"I want to apologise to Mason Rudolph, my teammates, our entire organisation, our fans and to the NFL. I know I have to be accountable for what happened, learn from my mistake and I fully intend to do so."
Garrett's violation went beyond unnecessary roughness and unsportsmanlike conduct rules and was punished for fighting, removing an opponent's helmet and using the helmet as a weapon, the league said in a statement.
The game was a physical contest with several penalised blows to the head to players whistled during the game by officials and the game culminating in an all-out brawl.
"We are extremely disappointed in what transpired last evening at the end of our game," Browns owners Dee and Jimmy Haslam said in a statement.
"There is no place for that in football and that is not reflective of the core values we strive for as an organisation. We sincerely apologise to Mason Rudolph and the Pittsburgh Steelers.
"Myles Garrett has been a good teammate and member of our organisation and community for the last three years but his actions last night were completely unacceptable."
Pouncey was punished for fighting, including punching and kicking an opponent. Ogunjobi was punished for unnecessary roughness for shoving an opposing player to the ground during an altercation.
'THAT IS INSANITY'
Additional disciplinary action will be coming for other players, including those who left the bench during the fight and potentially Rudolph for actions before he was struck.
"As an organisation, we are disappointed with what occurred last night near the end of our game against the Cleveland Browns," Steelers president Art Rooney II said.
"The actions of the players involved were not something that should be part of any football game."
Players have three business days to appeal the punishments under the league's collective bargaining agreement with players. All three are expected to appeal.
Friday's brawl was widely condemned throughout the NFL, with current and former players taking to Twitter to blast Garrett.
"That. Is. Insanity. Wow," was the verdict of Houston Texans star J.J. Watt.
Kansas City Chiefs quarterback Patrick Mahomes was similarly stunned: "Bro, I can't even believe that just happened."
Retired Houston star receiver Andre Reed said Garrett could have killed Rudolph, adding: "In the 17 years I played in the NFL, never been more disturbed by the end of a game."
Former Steelers defensive icon James Harrison said Garrett's attack was "assault at the least". "Six months in jail on the street … now add the weapon and that's at least a year right?!" Harrison wrote on Twitter.
Tim Younger, the agent for Rudolph, told ESPN "no options have been removed from the table" as far as legal options while Cleveland police told ESPN there is no investigation of the incident because Rudolph has not filed a complaint.
