Smith, 21, entered the plea as part of an agreement to have his felony weapons charge dropped. An Ann Arbor police officer stopped Smith for speeding on Oct. 7 and found his Glock 19 gun with three loaded magazines of bullets. Smith owns the gun legally and had registered the weapon, but he did not have a concealed pistol license needed to carry it in his vehicle.
He was arrested and released the same day, pending review for potential charges by the Washtenaw County prosecutor's office.
Defense attorney John Shea said Smith was applying for a concealed weapon permit at the time of the traffic stop and has one now.
Sentencing for Smith is set for Dec. 29, two days before No. 2 Michigan will face No. 3 TCU in the CFP Semifinal at the Vrbo Fiesta Bowl.
Smith, a team captain who has appeared in all of Michigan's games since the traffic stop and arrest, has had "no change" to his status, a team spokesperson confirmed to ESPN. After Smith was charged Dec. 1, Michigan athletic director Warde Manuel and coach Jim Harbaugh released statements supporting Smith.
"He is not and never has been considered a threat to the university or community," Manuel's statement read. "Based on the information communicated to us, we will continue to allow the judicial process to play out. Mazi will continue to participate as a member of the team."
Smith has 45 tackles this season, 2.5 for loss, while starting all 13 games at nose tackle.
According to the Detroit Free Press, Smith's sentencing likely will fall under the state's Holmes Youthful Trainee Act, which allows young adults to avoid having charges on their criminal record if they meet certain conditions.
The Associated Press contributed to this report.