Armagh-based Gilfresh Produce grows field vegetables and salads on 1,000ha, and also packs produce from contract growers, some under the Gilfresh brand.
It will use the facility to turn plant waste as well as cattle manure, chicken litter and silage into power for its own use, with the remainder being fed to the national grid. Process heat will be harnessed to heat the company's buildings.
Gilfresh founder Thomas Gilpin said: "The biogas plant will enable us to pursue our growth course on the one hand and our ecological goals on the other."
Biogas is among the renewable forms of energy production that currently attract incentives via Government feed-in tariffs.