Bed numbers at Hyson Green rose from 20 to 28 under the $2.5 million upgrade, which saw a new gym, larger range of services and full renovation.

Former AFP officer David Tonacia had stayed at Hyson Green six times since being diagnosed with post traumatic stress disorder on return from the Solomon Islands, where he was sent in 2006 to restore law and order.

He said the centre saved his life.

"The work they do here is invaluable, it recharged my batteries a little bit and each time I went I knew I was going to a safe place," he said.

"People form friendships in here too, so they have a bigger circle of support when they leave, and that helped me."

Hyson Green offers support for anxiety, depression, obsessive compulsion, panic attacks, psychiatric disorders and substance issues with mental illness medications.

It is the only private dedicated mental health service in the ACT, and is part of the national Catholic health care organisation, Little Company of Mary Healthcare.

Chair of the organisation John Watkins said there was strong and growing demand for private mental health care in the region.

"With eight new beds it gives us the capacity to provide extra services for the people in the ACT and beyond that who need that care," he said.

"There has also been a re-design of the service delivery with some more creative services available, and first class infrastructure for people to use as they may stay here for weeks."

Each room in the centre is single-bed.

The expensive cost and longer lengths of stay for private mental health patients posed challenges to the sector, Mr Watkins said.

But he said the extra layer of support eased some pressure off the public mental health system, which was accessed by more than 10,600 patients last financial year, according to ACT Health.

Little Company of Mary Healthcare saw an urgent need for more mental health services in the ACT in the findings of the 2016 Chief Health Officer's report.

It found one in five Canberrans reported having a mental health diagnosis in the past year, a rate higher than the national average. Anxiety remained the most common mental illness reported and had been on the rise since the 2007-2008 financial year.

Mr Tonacia and his wife Kate founded not-for-profit organisation Picking Up The Peaces, which raises awareness of PTSD in the ACT.

Mrs Tonacia urged people experiencing mental illness not to be afraid to seek treatment, saying it was a crucial part of a holistic approach to support and recovery.

"David has been hospitalised quite a few times, which has been very confronting for us and our children," she said.

"He actually stayed here recently just as the new centre was built, and the staff, the facilities and whole new day program were great."

"There is still so much stigma around mental health in the community, so over the years as we see it get more awareness, we hope support continues to grow, because we need more places people can go [to get help]."

Next to the Hyson Green Centre, Calvary's new private hospital is near completion and is on track to open to mid-2017, Mr Watkins said. The $72 million hospital will have 94 single-bed rooms, eight operating theatres and employ an extra 70 to 80 staff.