At today's announcement in Limerick were Munster stars Paul O'Connell, Jerry Flannery and Tony Buckley, as well Munster Rugby CEO Garrett Fitzgerald and Michael Whelan, Head of Sponsorship for Diageo Ireland, and Ken O'Dea, Regional Manager Limerick for Diageo Ireland.
Commenting on the new sponsorship, Michael Whelan said Guinness was delighted to extend its support of Irish rugby to include Munster.
"We are delighted to broaden our long-running support for Irish rugby to include both Munster Rugby and Thomond Park," he said.
"Guinness and Munster Rugby are two iconic Irish brands, with shared passion and pride in who we are and what we do. We are really looking forward to working with Munster over the coming seasons."
To celebrate the new sponsorship, Guinness organised an evening for Munster fans with Paul O'Connell and Anthony Foley at Peter Clohessy's pub in Limerick.
"This is just a small way to kickstart our partnership with Munster fans," Whelan added.
"They are central to the passion and success of the club, and we felt it was right and fitting that they should be involved in the launch of our new partnership."
Speaking on behalf of Munster Rugby, Garrett Fitzgerald said: "We are delighted to welcome Guinness on board as an official partner to Munster Rugby and Thomond Park.
"We recognise the great support Guinness has shown for the game of rugby in Ireland to date.
"We believe they will be an exciting and innovative sponsor of Munster Rugby and look forward to working with them closely to further enhance the Munster brand and the Munster experience for our fans."