The two organisations have announced today that both boards have approved a draft transfer of undertakings to enable the transition, which is expected to be completed later this year.
Talks between the two organisations began in July after CES invited other organisations to set out proposals for how they could help secure a strong future for the charity.
CES’s income has fallen from £2m in 2008 to slightly more than £1m in 2012, and it has made a loss in each of the past five years. Its accounts for 2013 have not yet been published, but are expected to show a loss of about £90,000, an NCVO spokesman said. CES is, however, expected to make a surplus in 2014, he said.
CES, which employs 12 staff, runs the PQASSO performance assessment tool, which has been used by more than 14,000 organisations.
The NCVO spokesman said the CES brand would continue to be used at least in the short term. He said the CES building in London would be sold and staff would move into the nearby NCVO offices near King’s Cross station.
Sam Matthews will step down as chief executive of CES. The NCVO spokesman said that her departure was not a redundancy, although CES was in the process of agreeing a settlement with her, and she would continue to advise the organisations on a consultancy basis after the transition.
Asked about the prospect of redundancies at CES because of the move, the spokesman said the details were still being worked on, "but it is worth reiterating that we are entirely committed to continuing all of CES’s products and services".
One CES board member is expected to become part of the NCVO board.
Sue Rossiter, chair of CES, said: "As a small organisation, we felt our activities would be much more sustainable if they were part of a bigger whole."
She said that the NCVO’s position "at the heart of the voluntary sector will help us to both reach and support more charities, and to develop new products and services to meet the changing needs of the sector".
Martyn Lewis, chair of the NCVO, said that bringing CES into the NCVO would complement his organisation’s strengths in consultancy, research and governance. "We want to be able to help our members by providing tools and expertise to support every aspect of their work," he said.