A US police officer who shot dead an Australian woman in 2017 was found guilty of murder on Tuesday by a Minneapolis jury.

Mohamed Noor, 33, who was fired from the Midwestern city's police force, was convicted of third-degree murder and second-degree manslaughter.

MORE NEWS Jury considers verdicts over killing of Sydney woman Justine Damond Ruszczyk

The jury, which was handed the case on Monday after three weeks of testimony from dozens of witnesses, acquitted the former officer of the most serious charge of second-degree murder with the intent to kill.

Noor was handcuffed and taken out of the courtroom in custody, according to US media reports.

Noor had testified in court that he shot Justine Damond Ruszczyk, an Australian who had moved to the US to marry her fiancee, to protect his partner because he had feared an ambush when responding to Ms Damond Ruszczyk's emergency call.

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But prosecutors insisted that the shooting was unreasonable and contrary to police department training policy.

Noor was taken into custody straight after the verdicts were read, just after 5pm.

The presumptive sentences vary from four years for the manslaughter charge to 12 and a half years for third-degree murder.

Family 'satisfied with outcome'

"We believe he was properly charged with a crime," Ms Damond Ruszczyk's father, John Ruszczyk, said.

"We are satisfied with the outcome. The jury's decision reflects the community's commitment to three important pillars of a civil society - the rule of law, the respect for the sanctity of life, and the obligation of the police force to serve and protect.

"We believe this guilty verdict strengthens those pillars. We hope this will be a catalyst for further change.

"We would like to note that we believe the conviction was reached despite the active resistance of a number of Minneapolis officers including the head of their union and either active resistance or gross incompetence of the BCA -particularly at the beginning of the investigation."

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Ms Damond Ruszczyk's fiance Don Damond thanked "everyone who has held us in their hearts and prayers - we have not walked this path alone"

“(Justine) taught us to live joyfully, she taught us to laugh and she demonstrated what it means to live from the heart," he said.

“She was a living example of compassion.

“In her life, she committed to transform humanity and her legacy is continuing that work today."

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Mr Damond said he thought the case showed "an egregious failure of the Minneapolis Police Department."

“Nearly two years ago my fiancee, Justine Damond Ruszczyk, was shot dead in her pyjamas outside our home without warning as she walked up to a police car which she had summoned,” Mr Damond said.

“Ironically the Minneapolis Police Department emblem on the squad door reads "to protect with courage and to serve with compassion. Where were these values that night? Justine tried to help.

“She called the police department to report sounds of a woman in distress. She called them because she needed them to protect with courage and serve with compassion.

“But that night there was a tragic lapse of care and complete disregard for the sanctity of life."

Jurors take less than a day to reach a verdict

Jurors took less than a day to reach a verdict in the trial of a former Minneapolis police officer who shot and killed the unarmed Australian woman.

The jury, comprising of 10 men and two women, gave their verdict on Tuesday evening.

The case went to the jury almost a month after jury selection began in a catastrophic shooting that prompted anger and disbelief in the US and abroad.

MORE NEWS Mohamed Noor takes stand in murder trial of Sydney woman Justine Damond Ruszczyk

Ms Damond Ruszczyk, 40, formerly of Sydney, was shot dead by Noor when she approached his police vehicle in an alley behind her Minneapolis home.

Ms Damond Ruszczyk had called 911 late on the evening of 15 July in 2017 after hearing a woman's screams and feared a sexual assault was taking place.

Noor and his partner, Matthew Harrity, testified Ms Damond Ruszczyk startled them.

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Noor feared they were targeted by an ambush.

Ms Damond Ruszczyk was dressed in a pink t-shirt with koalas on it, pyjama pants, no shoes and was carrying a glittery gold iPhone.

Noor targeted Damond from the passenger seat of the police cruiser he was in with his partner, Matthew Harrity.

"I want to extend my sincere apologies to the family and friends of Justine Ruszczyk Damond," Minneapolis Police Chief Medaria Arradondo said after the verdict.

"This was a sad and tragic incident that has affected family, friends, neighbours, the City of Minneapolis and people around the world, most significantly her home country of Australia."

Noor 'heartbroken' over shooting

Defence attorney Peter Wold told jurors the former officer was heartbroken over the shooting.

Noor testified that he believed there was an imminent threat after he saw a cyclist stop near the police cruiser, heard a loud bang and saw Harrity's "reaction to the person on the driver's side raising her right arm."

Noor added that when he reached from the cruiser's passenger seat and shot Ms Damond Ruszczyk through the driver's side window, it was because he thought his partner "would have been killed."

He said that after Ms Damond Ruszczyk approached the cruiser, his partner screamed "Oh, Jesus!" and began fumbling to unholster his gun.

Then, Noor said he saw a blonde woman wearing a pink T-shirt raising her right arm at the driver's window, identified her as a threat and fired.

Ms Damond Ruszczyk was wounded in the abdomen and died at the scene. Her last words were: "I'm dying," according to authorities.

'Sad and tragic' case

Ms Damond Ruszczyk had moved to the Midwestern city to marry her American fiancee Don Damond.

She had changed from her maiden name, Ruszczyk.

Her death caused outrage back home and her Australian family was in the courtroom for the trial.

The shooting also enraged many of the victim's neighbours, who mounted a campaign for police reforms.

The city's police chief at the time was forced to resign within days.

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"I want to extend my sincere apologies to the family and friends of Justine Damond Ruszcyzk," Minneapolis Police Chief Medaria Arradondo said in a statement after the verdict.

The chief called the incident "sad and tragic" and acknowledged that it had had an impact "around the world, most significantly in her home country of Australia."

"I will ensure that the (department) learns from this case," Mr Arradondo said.

Police officers involved in controversial shootings are rarely sent to prison because juries and judges are loath to second guess officers' life-or-death decisions made within seconds.

US trials have mostly resulted in hung juries or acquittals, which at times have caused civil unrest in American cities where racial tensions are already high.

Another Minnesota officer, Jeronimo Yanez, was fired from his job but acquitted after fatally shooting black motorist Philando Castile in 2016.