Certain incentives that can boost the deal up to $9.5 million were not revealed.
McDuffie put up a career-best 94 tackles last season for the Packers along with a sack, a forced fumble, three tackles for a loss, and three quarterback hits.
McDuffie was drafted by the Packers in the sixth round of the 2021 NFL Draft and, for the first time in his career, started all 17 games for Green Bay this past season.
The veteran, who is heading into his fifth year, has played in all but one game for the Packers in the past three seasons.
Meanwhile, teammate and fellow linebacker Eric Wilson, who was set to become a free agent with McDuffie, is still unsigned.
With McDuffie signing the new deal, it's uncertain if Wilson will return to Green Bay on a new deal when free agency begins.