The win, which the agency claims is worth £5 million, follows a three-way pitch against the radio specialist agency Eardrum and Heavenly.
The service, which is so far the only one to have both a number, 118 212, and a name, will compete against rivals such as The Number's 118 118 and 11 88 88.
Leith will launch three radio ads, using the voice of the art critic Brian Sewell, across commercial stations this week. They will run for the next year.
Jeremy Pyne, the managing director of Leith London, said: "In a market crammed with numbers, this one has a name as well as a number.
"Why 'Maureen'? Because research has shown that Maureens are the most helpful, dependable types of people and much nicer to deal with than numbers."
The ads for Maureen will aim to cut through consumer confusion by explaining carefully what the service does, how quickly it does it and what it costs.
John Perkins,the managing director of IRN, which supplies news to all commercial radio stations, said: "Launching a service by its name is a bold step. But we hope that, along with Brian Sewell's distinctive voice, it will bring the service to people's attention."
Media planning and buying is handled by Leith.