Dairygold is to create 115 full-time jobs by 2020 following a €117m investment in its dairy processing facilities at Mallow and Mitchelstown in Co Cork.
The expansion is also expected to create 400 temporary construction jobs.
The investments are supported by the Department of Jobs, Enterprise and Innovation through Enterprise Ireland.
It is envisaged that the expansion will also lead to a number of additional jobs in farming and indirect activity related to the company's output.
The investments are the result of the abolition of milk quotas from next April which will enable the dairy sector to expand.
Dairygold is a farmer-owned dairy co-operative, which processed over 960 million litres of milk in 2013, exporting to more than 50 countries.
Separately, the Irish Dairy Board has announced that it is to build a world-class centre of excellence for butter production and packaging in Mitchelstown as part of its strategy to grow the iconic Kerrygold brand.
It said the facility will have the capabilities to meet the evolving needs of its customers around the world.
The project is currently at the planning stage and a further announcement is expected in the coming months.