The chaotic scene unfolded in the town of 5,400 at about 6 p.m. MT Friday when a man in a black Dodge pickup truck rammed a police cruiser and then started shooting.
Chief Supt. Randy McInnes says the officers in the cruiser returned fire, killing the gunman.
McInnes says the female officer inside the police vehicle suffered serious leg injuries. A male officer was shot in the hand and another was hit in the face with flying glass. Both men were treated and released.
Meanwhile, officers were called to another scene where a man was found dead. They're not sure if there's a connection to the man in the black pickup.
Further details, including the gunman's name and a possible motive for the shooting, haven't been released.
The Alberta Serious Incident Response Team, which is called in when the actions of a police officer result in serious injury or death, is investigating.
St. Paul is about 150 kilometres northeast of Edmonton.