Former ACT Chief Justice Terence Higgins was endorsed for the role by an independent panel led by the Assembly's independent standards commissioner Ken Crispen, after a month-long recruitment process.

Speaker Joy Burch took the recommendation to the leaders of the ACT parliament's three political parties, as the legislation requires two-thirds of the Assembly to approve the choice.

However the Canberra Liberals told the Speaker they could not support the appointment because Mr Higgins used to be a prominent member of the Labor party.

Mr Higgins was the inaugural ACT Labor branch president in the 1970s and represented Gough Whitlam when he faced criminal charges in relation to the Loans Affair.

But Mr Higgins quit the party in 1990 ahead of his appointment to the bench.

He then served the ACT's courts until 2013, when he had to step down after reaching the mandatory retirement age of 70.

Mr Higgins then joined the Papua New Guinea national and supreme courts under laws allowing the appointment of non-citizen judges.

In 2016, Mr Higgins was among the five justices of the Supreme Court of Papua New Guinea who unanimously ruled that the Manus Regional Processing Centre breached the PNG constitution's right to personal liberty, and was thus illegal.

In a statement, Ms Burch said unless she received tripartisan support for the candidate, "it was determined that a vote would not be brought to the Assembly".

Pressed as to whether that meant the commission's start date could be pushed back, Ms Burch reiterated that she would not allow a vote to go ahead on a candidate until it was clear all three parties would endorse the appointment.

"At this stage we are unable to provide a timeline for an announcement of the Integrity Commissioner. The process is ongoing," Ms Burch said.

This could be a problem, as candidates were told during the recruitment process that they had to be around in late April to early May to help establish the commission - which is due to start work on July 1 - and to hire staff.

Chief Minister Andrew Barr, who supported the nomination, said the Liberals’ opposition had “set back the process of appointing a commissioner”.

“I think it really is a question for the Opposition as to why they’ve disregarded the legislative process and made the decision they have. It sounds very nasty and very personal,” Mr Barr said.

ACT Greens leader Shane Rattenbury said he was "dismayed" at the Liberals' "hyperpolitical stance".

“Former Chief Justice Higgins clearly meets the criteria set out in legislation. That includes that an appointee cannot have been a member of a political party in the past five years. As far as I can recall, no one proposed an amendment that would prevent the Commissioner from ever having been a member of a political party.

“If the Liberals are prepared to be this vindictive on appointments, it makes you wonder what would happen if they ever became the government.”

However Canberra Liberals leader Alistair Coe said it was paramount that the commissioner was “beyond reproach”.

“Whether we’re dealing with actual, potential or perceived conflicts I think we have to get it right and I think we owe it to all Canberrans to have a commission that everybody in Canberra can feel comfortable and confident with,” Mr Coe said.

“You have [the two-step process] for these very purposes where somebody could technically comply but there may be other issues that warrant further consideration but I do want to stress that I really want to avoid any interpretation that I’m reflecting on him rather than the process and the position.”

Mr Coe also said he would be prepared for the commission’s start date to be delayed until a commissioner they could all endorse could be found.

But Peter Conway - a friend of Mr Higgins', as well as a long-time Labor party member and former ACAT member - was outraged.

"I sat on the ACAT bench with [former Liberal attorney-general] Bill Stefaniak and no one would have dared to suggest we couldn't do the job because of our past associations," Mr Conway said.

The commission is set to investigate allegations of corruption involving public servants, politicians, and government contractors, with a focus on serious and systemic cases, and the most serious cases of misconduct.

The commissioner must have been a Supreme or Federal Court judge, a justice of the High Court, or a lawyer for at least 10 years, and have "extensive knowledge of and experience in criminal investigation or criminal adjudication, law enforcement or the conduct of investigations, or public administration, governance or government".

The commissioner cannot have been a politician, or a public servant in the past five years.

The strict criteria led to speculation last year that the ACT would be hard-pressed to find anyone to take up the job.

The ACT must also recruit a chief executive for the integrity commission.

An earlier version of this story incorrectly said the ACT must recruit a part-time inspector who will hold the commissioner to account. Instead, the Ombudsman will oversee the integrity commission.