Cowan moves from his current post of commercial director for Ireland on September 1, and will report to Andrew Morgan, president of Diageo Europe.
Cowan's appointment means Simon Litherland will be leaving his post as managing director of Diageo GB
A company spokeswoman said: “Simon is a very experienced and respected leader in Diageo, so it is with regret that, as a result of the European operating model changes, he will be leaving us.”
Cowan’s job will be “driving the commercial agenda and encouraging a customer-centric focus country-wide.”
He will also be responsible for relations with government and other external stakeholders.
David Smith, currently sales director for Diageo GB will be country director for Diageo Ireland, reporting to the western Europe chief operating officer John Kennedy.
The moves come after a marketing restructure announced earlier this week which saw the post of marketing director GB – held by Philip Gladman – axed.
Gladman was made category marketing director for white spirits, one of four category marketing positions covering the whole of western Europe.