McGregor had faced multiple criminal charges stemming from an altercation in April with other fighters.
As part of his deal he is required to undergo anger management treatment. The plea will not affect his US work visa.
In a statement outside the New York City courthouse, the 30-year-old thanked the judge and prosecutors “for allowing me to move forward”.
He will also be required to fulfil five days of community service and, in exchange, will be cleared of criminal charges.
McGregor had been facing 12 criminal charges related to the incident at Brooklyn’s Barclays Center on 5 April.
The charges against McGregor had included menacing, assault resulting in injury, reckless endangerment and criminal mischief.
The most serious charges carried a maximum sentence of seven years.