A Perth psychologist appointed by the Family Court has been found guilty of professional misconduct for writing an official report labelling a father's personality style as "psychopathic" without a clinical diagnosis.

Key points: The psychologist wrote an expert report tabled in a family court case

The psychologist wrote an expert report tabled in a family court case It resulted in the father being separated from his son when he was moved overseas

It resulted in the father being separated from his son when he was moved overseas The psychologist was fined $20,000 and banned from acting as an expert witness

In disciplinary action published by the WA State Administrative Tribunal, the psychologist has been ordered to pay a $20,000 fine and has been banned from acting as a single expert witness in either the WA or Australian family courts.

The disciplinary action against the psychologist, brought by the Psychology Board of Australia, stemmed from a report he wrote that same year as the only expert witness for a custody dispute heard by the Family Court of WA.

The report said that a nine-year-old boy at the centre of the dispute should be protected from his father, who he said had traits of a psychopathic personality disorder.

But the psychologist agreed, as part of the SAT mediation, that he had no evidence to support this claim and did not adequately consider the consequences of his report.

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"The report was of critical importance to the timely determination of the proceedings of the Family Court," the decision by SAT members Charlotte Wallace, Jack Mansveld and Alison Garton said.

"The Family Court was likely to place great importance upon the report because the [psychologist] had been appointed by the Family Court and not by a party to the proceedings."

The boy moved overseas to live with his mother in 2013 and was only recently reunited with his father.

The father said the case highlighted the failure of the Family Court system to properly scrutinise experts. ( ABC News: Robert Koenig-Luck )

The father — who, like the psychologist, the ABC is not naming due to the Family Law Act — welcomed the ban.

He first reported the psychologist to the Australian Health Practitioner Regulation Authority, which oversees the conduct of psychologists, in 2012.

The father said the case highlighted the failure of the Family Court system to properly scrutinise court experts.

"The fact that a professional doing the very important job of determining the lives and futures of our children cannot be named because of the draconian rules of the Family Court system is disgraceful," he said.

The psychologist, who stepped down as a Family Court expert in 2017, acknowledged his remorse and contrition for his professional behaviour and its consequences.