
The $1.4 million Macandrew Rd facility, named Rakiātea, will be a new base for the organisation to work from.
Director Mike Tonks said the Sisters of Mercy had held the land for many years and had partnered with Catholic Social Services in providing the 300sq m building.
"They spent many years [helping] families and children, and that's what we do here.
"So they passed on that mantle to us."
The organisation, which began with two staff in 1968, would continue using its current building nearby as well.
It had grown a lot since it began, and this was its biggest expansion, he said.
"We have about 23 staff and at the moment they are working in hallways and in very cramped, small offices."
There were also casual staff and volunteers.
Now they and the people using the service would have much more space.

It supported fathers navigating parenting, supported young mothers and supported relationships, including everything from giving parents nutritional advice to helping families deal with family violence.
It felt "fantastic" to have the new building open, Mr Tonks said.
The name Rakiātea was gifted by Ngāi Tahu and recognised the seeds of potential in everybody that could be developed or grown.
After months of preparation, the building was opened with a ceremony early yesterday morning attended by about 70 to 80 people.
A tapa cloth gifted by the Tongan community, which had been hung over the entrance, was pulled off to reveal a Māori carving above the doors.
The building was designed to be a multicultural and child-friendly space.
For example, rooms had names in different languages and bright colours were used.
Mr Tonks said Catholic Social Services was not just for Catholics — they were a resource for the whole community.
"It's for anybody, it's grace and goodness and respect for all people."