Chicken processing firm Moy Park is to acquire its rival O'Kane Poultry.
The combined firm will employ 8,500 people, with 5,000 of them based in Northern Ireland. Up to 30 redundancies are expected following the merger.
About 300 farmers who produce chickens for O'Kanes will now switch to Moy Park.
The expansion of O'Kanes turkey processing plant at Ballymena will continue. The new factory is expected to come on stream later this year.
Moy Park CEO Nigel Dunlop said the acquisition "will greatly increase our scale and capacity, including giving us a foothold in the turkey meat sector".
O'Kane Poultry chairman Billy O'Kane said the merger would mean "the future of our producers is assured".
Mr O'Kane, whose father founded the Ballymena-based firm in 1932, said it was "good news for the local agri-food industry and for the wider Northern Ireland economy".
The acquisition process is expected to take several months.
Mr Dunlop said: "Both businesses have strong brands and supply networks, and the central driver of this deal is to create an even bigger platform for market growth and to build on the significant sales and marketing achievements of both companies.
"We take our responsibilities as a major employer extremely seriously and the employees of both companies have been fully briefed on this development in advance of today's announcement," he added.
Ulster Farmers' Union president John Thompson said the two firms had "offered hundreds of farming families the opportunity to diversify their businesses into profitable poultry production".
"We have been working closely with O'Kane growers in recent times seeking to resolve a production problem which they are currently facing," he said.
"I am confident that we will be able to resolve this with Moy Park and ensure the growers are integrated successfully and enjoy a profitable future with the company."
Already processing up to three million chickens a week at its Dungannon factory, the aquisition of O' Kane Poultry at Ballymena will help make Moy Park one of the biggest chicken producers in the UK.
Moy Park is owned by Brazilian food giant Marfrig.