Justin Timberlake just sealed a plea deal in his DWI case … hammering out an agreement that does not involve drunk driving or even a criminal offense … he’s copped to a traffic violation.

The singer’s lawyer, Edward Burke Jr., and prosecutors just got the judge in the DWI case to sign off on the deal. The DWI charge is officially dropped, and Justin will cop to Driving While Ability Impaired … according to sources with direct knowledge.

Although the word “impaired” is used, it is NOT a drunk driving offense. As for the penalty, we’re told Justin will pay a $300 to $500 fine, and that’s it. The judge will set the exact amount of the fine during a hearing Friday, when the plea deal is officially before the court.

This is a major win for Justin, who was facing a serious criminal charge of Driving While Intoxicated following his June arrest in Sag Harbor.

Justin will still have his driver’s license suspended in New York … standard operating procedure because he refused to submit to a Breathalyzer test after he was pulled over by rookie officer Michael Arkinson. In NY, refusal to take a breathalyzer triggers automatic license suspension for a year.

The good news for Justin, he’s getting off with a slap on the wrist.

As we reported … Justin was arrested June 18 after cops say he blew through a stop sign and failed to stay on the right side of the road. He was charged with DWI but twice pled not guilty, and his lawyer maintained Justin was NOT intoxicated when cops arrested him.

Police said Justin failed field sobriety tests. JT claimed he only drank one martini. Despite body cam footage of the traffic stop, prosecutors apparently decided either the lesser charge was fair or a trial would be dicey.

Justin ended up cracking jokes about the incident on his tour.