Marston's has said that it will take over Brains' 156 pubs in Wales in a deal that will save 1,300 jobs.
The financial terms of the transaction were not disclosed, but Marston's said that the deal will address Brains' funding requirements.
The London-listed company has itself launched consultations on up to 2,150 job losses to deal with the sales hit from lockdowns, and, earlier this month, it called for more government support to bail out the sector.
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"As a consequence of the challenges of COVID, and in particular the recently announced more stringent additional trading restrictions in Wales, Brains' business has been under significant financial pressure," Marston's said.
The company said the deal is expected to add to its earnings in the first year after completion.
The transaction will also raise costs by up to £2 million, the company said.
Marston's, which is a two century old brewer known for its Pedigree, Hobgoblin and Lancaster Bomber beers, said that Brains' portfolio is complementary with its estate and that it intends to operate the pubs under the Brains' brand.