Red has been appointed as the company's retained agency after a four-way pitch and replaces incumbent agency Hotwire, which has held the account since 2005.
As part of the brief, Red will manage the brand's existing relationship with Grayling in France and Germany. The agency will also work on English language activity in the Middle East.
Catherine Eyres, PR manager at ACI Worldwide, said: 'With Red, we saw there was an opportunity to break from the trade press, where we have a good presence, and connect more with the business and national press.
'With a slightly off-centre approach, Red's presentation showed that our campaigns could look beyond what we had previously been doing.'
Red's technology practice was listed as the tenth largest in the UK in the PRWeek Technology League Tables.
ACI Worldwide provides electronic payment software for financial institutions, retailers and payment processors. On average, more than 75 billion transactions are made on behalf of more than 150 financial institutions globally by the firm in a year.
David Vindel, head of technology at Red, said: 'ACI's tools are at the heart of payments. Its software ensures people and businesses don't fall victim to financial crime.'