"It may be a small number of people who need this service, but at the moment we are not meeting that need," Ardern said.
"These people are sons and daughters, brothers and sisters. They and the staff who care for them deserve fit-for-purpose facilities that meet existing needs and this investment ensures that."
Peacock is due to be moved into the community soon, where he will live with specialist staff in a purpose-built home managed by provider Community Corrections.
He was moved to the Tawhirimatea unit at Porirua in 2007 and into the 'de-escalation' wing in 2010 because of psychosis and violence issues.
The new units will be built at the Ratonga-Rua-O-Porirua campus by the CCDHB and cater to those with intellectual disabilities or mental health diagnoses who are under the care of Mental Health Addiction and Intellectual Disability Services.
Health Minister David Clark said he expected the inquiry into mental health and addiction services to report back in October and that it would include "robust" recommendations for those suffering mental health issues.
Clark said the units would provide a greater quality of life for those who had previously been in in-patient services for lengthy periods of time.
"This will provide an opportunity for greater rehabilitative gains and the potential for reintegration into the community."
Clark said the six beds provided would meet the current need and there was room to expand it by four more units if those numbers grew.
He said it was possible there would be one or two in the next 10 to 20 years.
The ongoing costs were $4.8 million a year, which would come out of the existing funding arrangement with the DHB.
Mental Health Foundation chief executive Shaun Robinson welcomed the news of the new unit, saying he was pleased the government had recognised there was a need for the small group of people affected and was trying to meet it.
However, he said it would not make a material difference to the mental health needs of most, and he was more encouraged by indications from Clark that more measures would follow the mental health inquiry. He said a "shake-up" was needed in areas such as prevention and crisis management.
"Good mental health services are not about beds in hospitals," Robinson said. "The large majority of people who experience mental health problems are best supported and cared for in their communities. The earlier people get support and the more that support considers their whānau, housing, workplaces and real lives in the community, the better."
Mental health was one of the main campaign planks in Labour's election campaign. In January, Ardern announced an Inquiry into Mental Health and Addiction by former Health and Disability Commissioner Professor Ron Paterson.
At the time, Ardern said mental health issues and addiction were often closely linked.
The inquiry was to assess the current strengths and weaknesses of the community response to mental health, and the broader mental health system.
She also spoke about the need to address the suicide rate during the campaign, speaking of the impact a suicide in a friend's family had on the community she grew up in.
Media coverage of the event was almost scuppered after most outlets refused to agree to sign a wide-ranging Capital and Coast District Health Board confidentiality and non-disclosure agreement which threatened legal proceedings, a ban and trespass in the case of any breach.
The CCDHB eventually relented and allowed media in with a verbal undertaking to respect patient privacy.
