The agency has been handed an ongoing retainer to promote Zapp, a barcode-scanning app.
The service is being launched by VocaLink, the UK’s national payments provider, after a development cost of £100m.
The app is designed to offer real-time secure payments using just a user’s mobile phone and existing bank account.
Capella's role initially will be to raise the profile of Zapp among the financial and retail communities ahead of its consumer launch in 2014.
It will target news stories at national, broadcast and trade media, as well as running a profiling and thought leadership campaign.
Gareth Thomas, founder of Capella PR, said: ‘People have talked about mobile payment for years, but most solutions have lacked the credibility of Zapp, which is already backed by many of the major players in the industry. We will help Zapp secure even more widespread support.’
VocaLink is the company behind FasterPayments between bank accounts, and in 2012 processed more than 10 billion UK payments with a value of over £4.5tn.