The Cumbria-based Croftlands became a wholly-owned subsidiary of the Richmond Fellowship from 1 November.
It will remain a charity in its own right and will retain its name, contracts and brand.
Chris Graham, chief executive of the Croftlands Trust, said the move would enable the trust to make use of the Richmond Fellowship’s central services, such as human resources, IT systems that the trust could not afford to purchase itself, databases and quality monitoring systems.
He said there would be no redundancies as a result of the move and he would continue in his role as chief executive of the organisation, which had about 170 staff and reported an income of £4.5m in 2012.
The Richmond Fellowship had a group turnover of £40.8m in 2012 and employed about 1,000 staff.
Graham said that the move could help the charity to deal with possible cuts from one of its major funders, Cumbria County Council, which has said it needs to save £80m over three years.
"In the more medium term, we might have more pressures on our costs," said Graham. "The move helps us from a cost perspective, so we are better prepared for what might happen in Cumbria."
There will be no changes to the Croftlands projects as a result of the move, he said.
Diane French, director of operations, performance and quality at the Richmond Fellowship, will join the Croftlands board. Geoff Bland, chair of the management committee at Croftlands Trust, will become a member of the Richmond Fellowship’s board.
The Croftlands board has been reduced from 10 members to eight.
The trust underwent a restructure in February, which saw the number of senior management posts cut from four to three and moved to an area manager structure, which resulted in fewer managers, after Cumbria County Council retendered its contract framework.
The charity won a place on all three of the council’s frameworks, but there were "cost pressures" as a result of the retender, Graham said.
Derek Caren, chief executive of the Richmond Fellowship, said: "We have been proactively seeking formal partnerships with other charities in order to help us achieve our mission of making recovery a reality for the thousands of people we support each year.
"We believe that joining up with other successful organisations will allow us to offer a wider range of services, develop more innovative ways of providing support and reduce our costs."
A spokeswoman for the Richmond Fellowship said the charity was "continuing to seek active partnerships" and had an "informal working arrangement" with another organisation, but no other merger talks were under way.
The move comes after the Richmond Fellowship took over the County of Northampton Council on Addiction on 1 October. It acquired 2Care on 1 April 2011 and closed 2Care’s head office during 2012, according to the Richmond Fellowship’s accounts for the year.