The agency will focus on TV and radio activity for the bookmaker, which looks after much of its outdoor and print work in-house.
The pitch was handled by Oystercatchers. Chemistry meetings took place before Christmas and the final pitches were this week.
Paul Sweeney, the head of brand at Paddy Power, said: "We can’t wait to see how much trouble we can get into with our new friends at BMB."
Trevor Beattie, the co-founder of BMB, added: "We are delighted to be working with Paddy Power. It’s a marriage made in mischief."
During the process, the shortlisted agencies – BMB, Fold7, Grey London and M&C Saatchi – attended a meeting at the Tower of London.
CP&B had worked on the Paddy Power account since 2011, when it beat CHI & Partners and Mother, but did not repitch.
The brand also works with Lucky Generals on projects.