The British Association for Adoption and Fostering, which helped find substitute families for children, has closed and transferred some of its functions to other charities, with the loss of 51 jobs.
The BAAF said "significant changes and economic conditions" had made it impossible to sustain the organisation.
In England the Coram Group, a larger charity that helps children with a wide range of challenges, has pledged to take on a number of BAAF's functions.
The BAAF's latest accounts show it generated total income of £8.7m, including a government grant of £1m, in the year to 31 March 2014.
The financial pressures on the BAAF included "the loss of funding, high infrastructure costs and historic liabilities", as well as a decrease in referrals to its adoption service Be My Parent, according to a Coram spokeswoman.
BAAF and Coram have announced the creation of a new entity, called the CoramBAAF Adoption & Fostering Academy, to continue BAAF's role. No BAAF trustees will transfer to this entity or to Coram, according to the spokeswoman.