Errol Townsend, 31, of Sylvania, was arrested about 1am on September 27 at Potts Point and charged with possessing a prohibited drug and offensive behaviour in a public place.

The off-duty constable, who is attached to the Central Metropolitan Region, was suspended at the time of the incident.

He had 0.31 grams of MDMA in his possession.

He pleaded guilty in the Downing Centre Local Court on Tuesday and will be sentenced on November 27.