Detective Constable Jose Poonsawat of the Central South Command Unit pleaded guilty at Croydon Magistrates’ Court on July 12.
He has been released on bail and will be sentenced on August 23.
The incident occurred in December 2022 while Poonsawat was off-duty and involved him sexually touching a woman without her consent.
The investigation was conducted by officers from Bromley and the Met’s Domestic Abuse and Sexual Offences team.
With the conclusion of the criminal proceedings, the misconduct process will now begin.
Commander Seb Adjei-Addoh, who oversees policing in Lambeth and Southwark, stated, “My thoughts are with the victim, who has shown courage in reporting this sexual assault.
“Officers are rightly held accountable for wrongdoing by the courts.
“In this case, DC Poonsawat has pleaded guilty and now awaits sentencing.”