The Specialist Engineering Contractors Group and the National Specialist Contractors Council are expected to merge by next August.
The move is understood to have been prompted by the imminent retirement of NSCC director Grenville Weltch in July. Its main attraction is the pooling of the organisations' lobbying power.
SEC chief executive Rudi Klein has been tipped to become the chief executive of the new body. The post will not be externally advertised.
The two trade bodies fall under the umbrella of the Constructors Liaison Group, and the new body will retain the CLG name.
The SEC represents electrical and building services associations, whereas the NSCC represents mainly trade groups, such as painting and roofing associations.
The thinking is that the merger will create a more effective lobby unit
Klein, who declined to comment on speculation over his future role, said the move had first been discussed at a CLG board meeting in May, and that there was continuing discussion about a merger.
Klein said: "Any merger would have cost advantages but would also demonstrate a united single umbrella body for the whole of the specialist sector." Klein stressed that there was no timescale for the conclusion of the talks.
A CLG insider said the merger was likely to happen as soon as Weltch retired.
The source said the move would beef up the profile of the CLG. He said: "The NSCC and the SEC have not really had media recognition. The thinking is that the merger will create a more effective lobby unit."
The location of the headquarters of the new body has also been a matter of discussion. The SEC group is based in Bayswater, west London and the NSCC in Islington, north London.