Mary O'Callaghan, 50, now faces up to three years in jail. She has pleaded not guilty and is expected to appeal.
The case centred on a video recording, showing O'Callaghan hitting 35-year-old Alesia Thomas in the throat, abdomen and groin during the arrest in 2012.
Ms Thomas later lost consciousness and died in hospital.
A post mortem examination found traces of cocaine in her body, but the cause of death was listed as undetermined.
The jury in Los Angeles, California, reached the guilty verdict after two days of deliberations.
The police officer - who has been relieved of duty without pay after the incident - is now expected to be sentenced on 23 July.
Her lawyer Robert Rico said her client would appeal.
The defence team acknowledged that the footage showed an "ugly" scene, but said their client's use of force was "reasonable, justified and necessary" because Ms Thomas was not complying with the officer's orders.
The lawyers also stressed that O'Callaghan had an exemplary record during her 19 years of service.
The police woman went to arrest Ms Thomas on suspicion that she abandoned her two children.
The incident was caught on video by a dashboard camera in a police car.
O'Callaghan was not charged with killing Ms Thomas.
The US has recently seen a number of controversial cases when police officers used excessive force.
Recent data collected by the Washington Post newspaper suggests the number of people shot by US police is twice as high as official figures claim.
The paper said that during the first five months of this year, 385 people - more than two a day - were killed.
The number of black people was disproportionately high among the victims, especially unarmed ones.
A jury in Los Angeles has convicted a female police officer of assault for repeatedly kicking a handcuffed woman who died soon afterwards.