The agency has sealed a retained one-year contract to promote 3V, which is aimed at teenagers over the age of 16, and adults.
Instead of typing in credit or debit-card numbers, consumers buy a voucher (similar to a mobile phone top-up) that can be used on websites such as eBay and Amazon.
The service has already been piloted in Ireland, picking up 60,000 members.
The UK launch precedes a rollout on the Continent, which will be promoted by affiliate agencies.
Teamspirit director Jo Carr heads the account, reporting to 3V commercial director Niki Akhurst.
The agency said it would highlight 3V's anti-fraud credentials: the vouchers cannot be cloned and security details are kept separate from customers' email or mobile phone details.
