Billed as the largest single spend in the history of the Catholic Archdiocese of Canberra and Goulburn, the project dates back more than a decade and has been on hold since 2010.

It will bring together the headquarters of a wide range of Catholic services and agencies scattered across the ACT in two three-storey office buildings to be built above a 111-space underground car park.

The two buildings will be linked by an atrium and will include a meeting hall.

A complex of 44 independent living units for the elderly, which Canberra and Goulburn Archbishop Christopher Prowse said will create an on-site community and generate significant rental income, is integral to the development.

Archbishop Prowse said he had made the project a high priority as soon as he arrived in Canberra last November.

The ageing CatholicCare Offices and the derelict Haydon Centre, opened in 1962 and named in honour of Canberra's first Catholic priest, are being demolished to make room for the new buildings.

An existing presbytery, the home of the cathedral priest, is also being demolished and replaced.

"Even before I arrived here I was hearing about this project that had reached maturity in regard to its vision, with advanced architectural plans and construction plans already secured," Archbishop Prowse said.

The project had been close to sign-off when his predecessor Archbishop Mark Coleridge was transferred to the Brisbane Archdiocese in mid-2012.

A number of factors, including concern over a proposal to sell church property at Braddon to provide cash for the development, contributed to the delay.

That property will be retained but placed on the commercial rental market. The revenue from this, the on-site units and other properties will defray the cost of the development.

"We've done quite a lot of double and triple checking of the funding arrangements and we are quite confident it will go ahead," Archbishop Prowse said.

Helen Delahunty, the archdiocesan financial administrator, said green lighting the long awaited redevelopment was "a big deal".

"We don't have a lot of cash," she said. "It is the biggest thing we have ever done in terms of outlay, reorganisation and bringing people together. There will be between 50 and 100 people working from here and we have the Catholic Education Office across the road."

Ms Delahunty said the original idea had been to sell other assets to make the project cash neutral.

"That was not feasible for a number of reasons and we are now using assets in other ways," she said.

The underground carpark cannot be operated as a commercial facility and will be used by workers and churchgoers.

A key question that needs to be resolved sooner rather than later is what the new complex will be called.

"People are just starting to talk to me about that," Archbishop Prowse said. "I don't have a name in my mind but it will be given a name, either from a biblical background or a Catholic person from this part of Australia who has given conspicuous service. Stay tuned."

The Haydon Centre honours the memory of Monsignor Patrick Haydon, whose association with Canberra began with his appointment to Queanbeyan in the rural deanery in 1913 and ended with his death in the Canberra Community Hospital in 1949.

He had been the confidant to Catholic prime ministers James Scullin, Joe Lyons, Frank Forde and Ben Chifley and was the first pastor of St Christopher's parish, Canberra.

Fast facts

Title: St Christopher's Cathedral Precinct Project

Cost: $35 million.

Start: December 2014/January 2015.

Completion: December 2016.

Key features: