This appointment follows a change in Diageo’s marketing department structure, which began in June and saw the global marketing function move from a brand focus to category management.
This resulted in the appointments of David Gates to the role of global category director for whisky, and Ed Pilkington as global category director for vodka, gin and rum.
Beer is the second-largest category after whisky within Diageo, led by global beer brand Guinness and supported by a diverse portfolio of local brands such as Red Stripe, Windhoek and Harp.
Chief marketing officer Andy Fennell said: "We believe viewing our business through a category lens is the right way to source growth for Diageo, and Brian brings to this new role a wealth of beer, marketing and commercial knowledge and know-how.
"In this new category approach, we believe we can target significant opportunity for our beer business and allow us to reach our targets for our beer portfolio," he added.
Duffy has been with Diageo for 29 years and has led the Guinness brand to steady, year-on-year growth since 2004. In his new role, he will be responsible for devising the total category strategy and for identifying new growth opportunities.
Duffy will maintain his position as Diageo Ireland chairman and will continue to be based in Dublin. Diageo will also be appointing a Guinness global brand director to report to Duffy.