The retiring head of the Family Court in Western Australia has launched a scathing criticism of the Federal Government's plan for reforming the family law system, arguing it has been dreamt up by accountants and not the people who work in the sector.

The Federal Government is hoping to merge the Family Court and the Federal Circuit Court into one body, promising it will alleviate the cost pressures and lengthy delays vulnerable families face when turning to the courts to help resolve disputes.

Justice Stephen Thackray is retiring in January, having announced his departure earlier this year following a 21-year career on the bench.

He told an audience at the University of Notre Dame in Perth on Thursday night he had heard the Coalition's efficiency arguments before, when the Howard Liberal government established the Federal Circuit Court (then known as the Federal Magistrates Court) in 1999, and noted judges had issued warnings at the time.

"Those of us who have been around for a while could not help but recall on hearing these remarks that the Attorney-General who created the current "split family law system" had, almost 19 years earlier, used eerily similar words when proclaiming that his new system would provide a "quicker, cheaper option" for family law dispute resolution," Justice Thackray said, in a copy of the speech seen by the ABC.

"The split system has therefore stumbled along until 2018 when we are now informed, on the basis it seems of a report from a firm of accountants, that the flaws in the system are not entirely the fault of the government that created it, but rather the inefficiency of the court whose Chief Justice accurately predicted the outcomes we now see.

"We should be wary of law reform being driven by statistics produced by firms of accountants in the guise of measuring or quantifying the productivity of the courts."

Justice Thackray was referring to a number of reviews into the system, including one study by consultants PwC into potential efficiencies that could be achieved under any merger of the courts handling family disputes.

Thackray's parting shot comes after dumping from key role

Justice Thackray was dumped as the head of the Family Court's national Appeals division in March, under the short tenure of Chief Justice John Pascoe.

His replacement on the Appeals bench was the head of the Federal Circuit Court, William Alstergren — who was named as Chief Justice Pascoe's successor on Thursday.

Many in the legal community have raised concerns the merger proposal will fail to deliver its promised outcomes, and is being rushed through without proper consultation with those working in the family law system.

Further criticism has been levelled at the Government for pushing ahead with the merger before a full review of the family law system delivers its findings next year.

The retiring judge also levelled criticism at political appointments to organisations such as the Administrative Appeals Tribunal (AAT).

He argued Australians should not necessarily doubt the competence of people given roles on the tribunal, but suggested their credibility could be questioned if they had strong ties to the political establishment.

"The public needs confidence that those appointed to judicial office owe fidelity to the law, not to those who appointed them," he said.