Mental health charity Community Options has become a subsidiary of Heritage Care, which supports vulnerable people, and will manage its mental health services.
The charities said the merger would bring cost savings by sharing overheads, such as human resources, insurance and training.
Twenty-three staff will transfer from Heritage Care, which employs roughly 1,700 people, to Community Options to work on front-line mental health services.
Three of Community Options’s 138 employees will transfer to Heritage Care’s offices to provide corporate services support. The charities said the merger would not lead to any job cuts or redundancies.
Stephen Lenton, director of HR and organisational development at Heritage Care, said there were mutual benefits from the merger.
"Mental health has always been a small part of our service so we felt it was best to find a specialist provider to merge with," he said.
The move would create "evolutionary rather than radical change", he said.
Chris Mansi, chief executive of Community Options, said the merger would help it to expand into new geographical areas and build on its ethos of providing personalised mental health services.
"We are looking at the economic climate and are being encouraged to look at where we could be more efficient in how we deliver services to people," she said.