Ontario Justice Tim Lipson said the Sept. 6, 2008, arrest of the woman on a charge of public intoxication was not warranted, as she was not a threat to herself or others.
But Lipson said the Crown failed to prove beyond a reasonable doubt that Desjourdy's conduct during a strip search in the cellblock was unreasonable and committed in a sexual nature.
Lipson said he was satisfied Desjourdy conducted the strip search with the valid purpose of checking the woman for possible weapons.
The woman, who can't be identified because of a publication ban, was in court to hear the verdict. She declined to be interviewed after the verdict was announced.
As Desjourdy walked out of the courtroom, about 50 police officers who had gathered outside applauded.
Incident prompted debate
Desjourdy was charged after the province's Special Investigations Unit investigated an incident in which the officer used scissors to cut off the bra and shirt of a woman arrested for public intoxication.
The strip search was captured on surveillance video, which was released to the public by a judge.
The video ignited a debate about whether the strip search was proper police procedure or sexual assault.
Discreditable conduct charge remains
Desjourdy still faces a charge of discreditable conduct under the Police Services Act. A date for that hearing has not yet been set.
Ottawa police Chief Charles Bordeleau said in a statement his force "respects the court's decision."
"The Ottawa Police Service will not be making further comment on today's decision nor the review and upcoming process regarding the PSA charge of discreditable conduct."
The woman who was strip-searched has also launched a $1.2-million lawsuit against Ottawa police.