Bradley Robert Stevenson, 27, appeared in the ACT Supreme Court on Monday, charged with stalking, possessing an offensive weapon and two counts of property damage.

While the Calwell man admitted the allegations against him, he pleaded not guilty by reason of mental impairment to all charges.

A summary of agreed facts shows Stevenson loitered near the victim's worksite in Isabella Plains on August 25 last year and watched her as she was landscaping a nature strip.

He returned there the next day and approached the woman while holding a knife.

The victim fled in her car, followed by Stevenson in his.

When she had to stop at a red light, Stevenson rammed his vehicle into the back of hers and caused the pileup.

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Justice Michael Elkaim said the woman did not know what to do after the impact, so she "sat in the driver's seat and screamed".

"A matter which is not covered in the above summary is the detail about how terrifying the events must have been to the victim, the complainant," Justice Elkaim said.

"I have no doubt that on both [August 25 last year] and on the following day, she would have experienced feelings ranging from concern to outright terror."

Paramedics attended the scene and took the woman, who had scratches on her lower legs, to hospital for examination after she reported feeling pain in her neck and chest.

Because Stevenson admitted the conduct in question, the central issue in court on Monday was his defence of mental impairment.

Justice Elkaim said he had received reports and letters on this subject from two psychiatrists, including Associate Professor John Kasinathan.

Associate Professor Kasinathan said Stevenson was probably "harbouring under significant impairment" at the relevant time because of "poorly treated schizophrenia".

"This severe untreated psychiatric illness impaired Mr Stevenson's capacity to judge whether his actions were right or wrong because he held a delusion that he was persecuted by a group including the alleged victim, and he heard the victim's voice and another voice commanding him to hurt her," the expert wrote.

The other psychiatrist diagnosed Stevenson with "a psychotic disorder".

Justice Elkaim said there was "no competing opinion" to those offered by the two experts, so he was satisfied Stevenson was impaired to the extent the man was not criminally responsible for his actions.

The judge therefore entered verdicts of not guilty by reason of mental impairment in relation to each charge.

He ordered that Stevenson submit to the jurisdiction of the ACT Civil and Administrative Tribunal, which has the power to make decisions about his mental health treatment.

Stevenson, who was already on bail, will remain subject to conditions while this takes place.

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