The Stockholm District Court ruled the officer had no right to be so violent as she "was not in a situation of imminent danger or threat, as there was no indication the man would attack her".
The incident occurred on a Friday night in July central in Stockholm, and was captured on film by a passerby. A film clip of the incident shows the policewoman beating a drunken man at least 14 times with a baton while her dog attacked him.
The victim, who fell to and remained on the ground for much of the video, had mumbled that he would bomb the street. When he finally let go of the dog he howled at the police woman "Are you totally stupid?".
The video, published by the Dagens Nyheter newspaper, made headline news across Sweden and sparked discussions about the use of force by the country's police officers.
In Monday's ruling, the court also found there was no visible emergency that warranted the officer's use of her baton, adding that she had used "extremely excessive force".
"By letting the dog attack and bite the man and by hitting him with her baton afterwards, the police woman has ensured she was guilty of assault," the court reasoned.
The prosecutor described the victim of the attack as "confused" and added that he was suffering from mood swings at the time of the incident. The altercation had been triggered by the man's previous actions around the city, during which he had broken a window, and hit several people. Charges have also been filed for these crimes.