Antrim and Newtownabbey Borough Council has been informed the facility is planned to open in 2026.
It will replace the current Holywell Hospital and the Ross Thomson Unit at the Causeway Hospital in Coleraine.
East Derry MLA Ms Hunter said: “I was delighted to hear details of this plan which will transform the way patients with acute mental health conditions are cared for in the North.
“Our current in-patient facilities are very outdated and the planned new hospital would allow us to bring our facilities into the 21st century.
“We have learned much about the best ways to treat people with mental health conditions since our current hospitals were built and I am glad to hear this has been taken into consideration in the plans for the new Holywell Hospital. If people are to get well then their environment has a key role to play in this, people need to be treated with dignity and respect and not feel that they have been locked up or put away and that their condition is something they should feel ashamed of.
“While the planned 134-bed building is a good start, the sad reality is that we have thousands of people with mental health issues currently across the North.
“While not all of these will require in-patient treatment, we need to ensure that we have the capacity to provide for those that do. Proper centres to treat patients of all kinds with mental health disorders must form a key part of Health Minister Robin Swann’s mental health action plan. Quick access to the right treatment plays a key role in helping people with severe mental health conditions get on the road to recovery.”