Tullamore Drew sells 600,000 cases a year
The distillery company William Grant is to buy the spirits and liqueur business from the Irish company C&C group for around £250m.
The brands include Tullamore Drew, Carolans, Frangelico and Irish Mist.
William Grant is more than 100 years old with brands including Glenfiddich, Grants and Hendrick's Gin.
Stella David, chief executive officer of William Grant, said: "We have been looking to further develop our non-Scotch portfolio."
She added: "Irish whiskey is a natural fit and C&C's spirits business provides a unique opportunity to acquire a number of significant brands and enter the highly desirable and dynamic Irish whiskey category.
"We shall make significant investment in Ireland and invest in the long-term value growth of the brands, including Tullamore Dew Irish Whiskey which, at 600,000 cases, and given its potential, will become a core global brand in our business."
The deal needs shareholder approval but William Grant expects the deal to be completed by the end of June.
C&C, which is based in Dublin, bought Tennent's lager in a deal worth £180m last year.
It also owns Magners and Bulmer cider.