This is the fourth Diageo brand for Mother, which also works on Pimm's, Tanqueray and J&B.
It won the account following a closed pitch process that kicked off earlier this year.
Diageo’s other roster agencies include Abbott Mead Vickers BDDO (Guinness) and Adam & Eve/DDB (The Singleton Scotch).
Diageo split with the previous agency, Bartle Bogle Hegarty, in May. At the time, it claimed it was bringing the advertising for Gordon’s and Baileys in-house, but the drinks giant changed its mind and began approaching agencies.
Garbhan O’Bric, the Baileys global brand director, said "We are delighted to be working with the team at Mother. We were bowled over by the strategy and creative that they demonstrated, we felt that the people behind the agency were wonderful and we are confident that Mother has all the right ingredients to become the perfect long-term partner."
The Baileys win is the result of a pitch run out of London and New York Mother offices and the business will be led out of London.
Anomaly London won the global creative account for Gordon’s gin in August. It also handles Johnnie Walker.
Michael Wall, the global chief executive of Mother, said: "It’s fantastic to add Baileys to our existing Diageo brands. This is a cherished and longstanding client relationship and we have some great global work in the making.