Plans to build a new 40-bed hospital for people with learning disabilities alongside the high-security Ashworth Hospital have been approved.
Full details of the £33m low-security unit are yet to be revealed, but Sefton Council gave Mersey Care NHS Foundation Trust outline approval on Thursday.
Councillor Daren Veidman said it would both help "some of the North West's most vulnerable" and bring the Maghull area "considerable economic benefits".
The trust said it was "delighted".
"Maghull has a long and living history of hospitals providing mental healthcare dating back more than a century, so we're delighted to be building on that tradition," executive director Elaine Darbyshire said.
She said the new unit would "offer world class care in a therapeutic environment" and help "provide a new model of care for complex patients across the North West".
"Ultimately it will also cement the future of Maghull Health Park as a centre of excellence, as well as help boost the local economy and jobs," she added.
The building would be the second new facility to be built alongside Ashworth, as the medium-security Rowan View facility is approaching completion.
A spokesman said it would cater for up to 40 men and women, each of whom would have "their own bedroom with en-suite bathroom".
He added that it was hoped the new facility would open by summer 2023.
Ashworth Hospital is one of only three psychiatric units in England providing services for patients who "require treatment and care in conditions of high security", the trust said.