The final stage of the justice precinct project will now be completed by next September, ACT Attorney General Gordon Ramsay told the Legislative Assembly on Tuesday.

The project was originally slated for completion by the end of this year, and the first stage was to be finished by the end of last year.

But the deadline was pushed back in May, with stage one completion due in August-September and stage two to be finished in the first half of 2019.

Mr Ramsay told the Assembly the construction of stage one had presented some challenges given the proximity of the building work to working courtrooms.

However, he said the same number of courtrooms had been available during the construction phase as before the project began, and construction had not impeded the work of the courts.

"Like stage one, the stage two works will be managed so that there is minimal disruption to the courts’ functions and it is expected that stage two will be completed in the third quarter of 2019," Mr Ramsay said.

Stage one of the project reached technical completion on September 25, with its first sitting on October 15, although some of the façade facing Vernon Circle was still missing.

Mr Ramsay said he had been advised the arrival of the missing cosmetic panels was imminent.

Stage one of the project involved the construction of the new four-storey building fronting Vernon Circle, refurbishment and reconfiguration works in the existing Magistrates Court building, and a new entrance foyer linking the two existing buildings.

Stage two includes the refurbishment of the two remaining courtrooms in the heritage court building, as well as construction of mediation suites, hearing rooms and spaces for justice support groups.

When stage one of the precinct opened earlier this month, Chief Justice Helen Murrell said the construction phase had been "a great juggling act", but the wait had been worthwhile.

She said the new facilities would improve court productivity and wait times for defendants.

"We've got all the facilities we need, for now and into the future so we're absolutely delighted," Chief Justice Murrell said.

Mr Ramsay prefaced his comments with a reminder the courts project had been undertaken as a public private partnership, where the private sector consortium wears the cost on any delays.

It's the second time in a week that the government has been forced to come out and admit a project being delivered as part of a public private partnership has been subject to delays.

Transport Minister Meegan Fitzharris revealed last week the light rail project - another public private partnership - is months behind schedule.

The announcement came after Transport Canberra's latest annual report showed the project missed nearly all of its milestones by several months.

While a Transport Canberra spokesman suggested the construction schedule was dynamic and the milestones were just estimates, it is understood the delays relate to the complexity of the project and safety.

It means Canberra Metro will miss out on its first availability payment - worth millions of dollars.