Synlait Milk is buying Canterbury's Dairyworks for $112 million as part of its push into the consumer market.
The speciality milk producer said Dairyworks was a good fit for its everyday dairy strategy, and complemented the recent purchase of cheese manufacturer Talbot Forest.
Dairyworks supplied New Zealand with almost half of its cheese, a quarter of its butter, as well as milk powder and Deep South ice-cream.
It also owned the Dairyworks, Rolling Meadow and Alpine consumer brands, which supplied supermarkets in New Zealand and Australia.
Synlait chief executive Leon Clement said Dairyworks added to its value chain, while giving it access into Australia where Dairyworks presence was growing.
"Opportunities exist in both businesses to streamline supply chains and enhance our competitiveness," he said.
"It gives us the ability to optimise how we process milk solids and get the most value from our supply of milk."
Dairyworks would continue to operate as a stand-alone business under the Synlait umbrella, with its chief executive Tim Carter reporting to Mr Clement.