Minneapolis police officers will be required to turn on their body cameras as soon as they start responding to 911 calls, part of a policy overhaul announced on Wednesday as fallout continues from the fatal shooting of an unarmed Australian woman by an officer who was wearing a camera but not recording.

“What good is a camera if it is not being used when it may be needed the most?” said Medaria Arradondo, the city’s acting police chief.

Questions about the non-use of body cameras, which were rolled out in Minneapolis last year to much fanfare, have swirled since Justine Damond, the Australian woman, was shot dead in a dark alley by Officer Mohamed Noor on July 15.

Ms. Damond had twice called 911 that night to report what she feared was a sexual assault happening outside her home. Officer Noor’s partner, whose body camera was also turned off, told investigators that he heard a loud noise before Officer Noor fired a shot from inside their patrol car, fatally striking Ms. Damond.

Her death, the latest in a string of high-profile police shootings in and near Minneapolis, reverberated across the world, prompting protests on the streets of Minnesota and a rebuke from the prime minister of Australia. The Minneapolis police chief, Janee Harteau, was forced to resign last week, the mayor has faced calls to quit and some in the city have called for a broad rethinking of law enforcement.

“This is bigger than simple change to a body camera policy,” said Jillia Pessenda, a candidate for Minneapolis City Council who said Wednesday’s changes were a good step. “We have to look at how do we overhaul a policing system in our city that is not working.”

The shooting of Ms. Damond has so far defied explanation, with no known video images and Officer Noor declining to speak with state investigators. Mayor Betsy Hodges, a Democrat who is up for re-election in November, has said that the officers’ body cameras should have been on.

“One of the toughest things that all of us in Minneapolis have had to face is that after the time and the money and the energy that we put into making sure that body cameras were in place,” Ms. Hodges said, “we did not have body camera footage in an incident where it mattered a great deal.”

The new policy, which takes effect on Saturday, gives officers a specific list of situations when they must turn on the devices — when being sent to a scene, when “self-initiating a call,” when “any situation becomes adversarial,” among others. It also codifies that discipline, up to and including termination, can be meted out for violations.

Mike Padden, a lawyer representing a woman whose two dogs were shot by a Minneapolis police officer this year in an episode that was recorded on a body camera, said that the “department deserves a lot of credit that they’re moving this quickly” to revise a policy that had shortcomings.

“It will take away wiggle room for officers’ depictions of what happened in the field,” Mr. Padden said, “and I think it’s going to cause them to behave better in the field as peace officers.”

Lt. Bob Kroll, president of the union representing rank-and-file Minneapolis officers, said in a statement that the “rapid changes to the body camera policy initiated at the direction of Mayor Hodges are a knee-jerk reaction and politically motivated.”

Lieutenant Kroll called Ms. Damond’s death “a terrible tragedy,” but claimed that “the officers were in compliance with existing body camera policy.”

In Minneapolis and elsewhere, body cameras have been promoted as a way to increase accountability and to ensure that officers are following the law. But the body camera policy adopted in Minneapolis last year was not as sweeping as some had hoped. And before Ms. Damond’s death, a local news report found that Minneapolis officers recorded relatively little body camera footage, averaging around five to six hours each during one month this year.

“There are some officers, quite frankly, that are not using them nearly enough,” Chief Arradondo said on Wednesday.

Chief Arradondo, who has been nominated by Ms. Hodges to lead the department, said supervisors had been trained in recent weeks on auditing officers’ use of body cameras, and that work to update the camera policy had been underway before Ms. Damond’s death. The city is also installing technology to automatically turn on body cameras when a police car’s emergency lights are activated.

“We need to build and regain our community’s trust,” Chief Arradondo said. “Body-worn cameras is a tool. It’s not everything. It’s only a tool.”