Brewer Marston's is to merge with Carlsberg's UK arm, uniting ales such as Pedigree and Hobgoblin with Danish Pilsner and Somersby cider.
The joint venture is valued at £780m, with stock market-listed Marston's taking a 40% stake in the merged firm.
The deal involves Marston's six breweries and distribution depots, but not its 1,400 pubs.
The new Carlsberg Marstons Brewery Company will create "synergies and productivity" benefits, Marston's said.
Marston's employs a total 14,000 people.
Carlsberg UK will put its Northampton brewery, London Fields brewery, and national distribution centre into the joint venture. Marston's will put in its six national and regional breweries - Marston's, Banks's, Wychwood, Jennings, Ringwood and Eagle - and 11 distribution depots.
The deal means Carlsberg will have access to Marston's pubs to sell a wider range of brands.
Ralph Findlay, chief executive of Wolverhampton-based Marston's, said the joint venture brings together companies known for heritage and brand portfolio.
Tomasz Blawat, managing director of Carlsberg UK, said the deal enables the companies to offer "a bigger beer portfolio of complementary international, national and regional brands".
The coronavirus lockdown means UK pubs are closed, with many in the industry saying that a mooted re-opening with a two-metre rule for customers would not work. Some pub operators have suggested that a one-metre rule might be a better compromise.