The one-year old Solicitors Association has merged with the 30-year-old British Legal Association.
Members from both groups, who were due to meet and formally amalgamate over the weekend - after The Lawyer went to press - are vowing to continue campaigning for a split in the representative and regulatory functions of the Law Society.
Surrey practioner Anthony Bogan established the SA 12 months ago as an alternative to the Law Society and then unsuccessfully campaigned for president in the society's elections.
Bogan, who is a society council member, said joining with the BLA made sense.
"There were two organisations with parallel objectives and it seemed a duplication of effort and a waste of resources," he said.
The new organisation, which will retain the BLA title, will have around 2,200 members, 1,037 of whom will come from the Solicitors Association.
Bogan was expected to be elected as BLA vice chair at the weekend, with current chair Alex Alagappa retaining his position. Alagappa was not available for comment on the amalgamation.
Largely representing high-street solicitors, the enlarged BLA will seek to lobby the Law Society on issues of concern, such as the need for Solicitors Property Centres.
"We will aim to keep them on their toes," said Bogan.