No financial details were given but media reports have spoken of a "cut-price" deal for a tournament that starts in February.
The Times newspaper said Guinness would pay six million pounds ($7.66 million) in the first year, compared to a reported nine million paid by NatWest, but with the sum growing annually to double by the final year.
Guinness already sponsors the PRO14, involving professional teams from Ireland, Scotland, South Africa and Wales, and has partnerships with Irish clubs Leinster and Munster as well as the four home unions.
"This announcement affirms our long-standing support for the game of rugby and cements our position as one of the world’s biggest rugby supporters," said Mark Sandys, who oversees Diageo's beer brands.
($1 = 0.7834 pounds) (Reporting by Alan Baldwin, editing by Toby Davis)
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