The agency, which won the brief without a competitive pitch, will be responsible for creating ways of connecting J&B with its core 18- to 24- year-old market.
M&B's work will initially focus on ideas for the Spanish market, then Mexico. The brief is to create ideas beyond traditional advertising that will bring the brand to life.
M&B secured a similar international role for Unilever this summer, briefed to develop communications channels with consumers outside traditional advertising.
J&B is the number-two Scotch in the world and number one in Europe, but it is trying to appeal to young drinkers against stiff competition from white spirits and ready-mixed drinks.
Iain Kennedy, J&B's global brand director, said: "With its work for other brands, M&B has proven it can deliver powerful ways of connecting brands with their consumers. This is precisely the kind of brand engagement that J&B needs right now."
Paul O'Neill, a partner at M&B, added: "The brand is one of the most famous. The brief is challenging. And this client is hungry for new ideas."
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.