Snowball has set out her agenda as driving greater cross-industry support for the AA and ensuring its key messages hit home with the Government and opinion-formers.
She succeeds Andrew McGuinness, a founding partner of Beattie McGuinness Bungay, who steps down on 1 June after three years in the role, and has promised to build on his work.
Snowball will work alongside the AA's chief executive, Tim Lefroy, and its president Gavin Patterson, the chief executive of BT Retail and a director of BT Group plc.
Snowball said: "The AA has begun an important transformation, in line with the step-change that we are seeing in the issues and opportunities across advertising. We've an ambitious AA team, energetic support from practitioners and a sharpened narrative on why advertising matters. My job is to build on that good work and bring fresh momentum to the case for our industry. I can't wait to get started."
Patterson added: "Cilla shares our vision of an ad sector that is more confident, cohesive and better understood. We're making great progress and, with such high-calibre support arriving, we can only move even further, faster."