The company says the decision to use the Farm name is due to the perception of Leith London as a satellite of the original Leith Agency in Edinburgh, whereas Farm is seen as an established, standalone agency.
John Rowley, chief officer of the Farm, said: "Farm already have a reputation for fresh thinking and are becoming increasingly established within the UK marketing scene. We considered a third name, but ultimately it seemed far more sensible to build on the excellent start that Farm has made".
Uniting under the Farm name overcomes previous conflict issues that arose between the two Leith offices. For instance, the two offices count different Coors Brewer brands as clients. Edinburgh handles Grolsch, Worthington and Caffreys, while London handles Carling and Reef.
The Leith Agency in Edinburgh and Farm will continue to share resources and pitch jointly when relevant, but will now have a free rein to pursue individual opportunities.
Owen Lee, creative partner at Farm, said: "Our culture is the reason we get up in the morning and the reason our clients buy us. In Leith London, we found a fantastically talented group of people who think the same way that we do, they just happen to be doing it under a different name."
The agency is set to relaunch at the end of August with a new visual identity and new offices. The identity will reflect the "maturity of the bigger combined agency". The company said there is not expected to be any redundancies on either side.
The merger will create an agency with combined billings of around £42m and 65 staff.
The Cello Group, which already owned Leith, acquired Farm in early June. It said it hoped the merger would enable it to diversify into digital, brand experience and new media channels.
Earlier this month, Cello acquired a 50.1% share in digital agency Oomph for £300,000.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .