The attorney for Assemblyman Steven Katz entered the guilty plea on his behalf to a parking ticket. Katz did not appear in court in Coeymans.
He must serve 20 hours community service and pay a $75 fine.
The case will be adjourned in contemplation of dismissal if he completes the court ordered community service by June and stays out of legal trouble.
Katz' attorney said the case was downgraded to a parking ticket. The attorney continues to dispute the marijuana component.
Troopers say the 59-year-old Katz, of Mohegan Lake, was stopped in mid March in Coeymans, south of Albany, for driving 80 mph on the highway with a 65 mph speed limit.
They say he had less than 25 grams of marijuana and was given an appearance ticket for the violation.
Katz voted against the legalization of medical marijuana during a vote last June. It passed 91-52, with most Republicans voting against it.