The part-state owned lender is one of 18 banks behind VocaLink, which is being sold to Mastercard in a deal worth up to £869m.
VocaLink runs services for banks, including Bacs, Faster Payments and Link cashpoints, as well as mobile app Zapp. It processed more than 11 billion transactions last year with a value of £6 trillion and reported revenues of £182m in 2015.
The deal comes after the Payment Systems Regulator called in February for banks to sell their stakes in VocaLink to “open the market and allow for more effective competition and innovation”.
It said at the time that banks should loosen their grip on the way payments are processed, with VocaLink processing more than 90 per cent of salaries, over 70 per cent of household bills and almost all state benefits in the UK.
Mastercard is acquiring a 92.4 per cent stake in the service for £700m, with a further potential £169m due if performance targets are met.
RBS is one of the largest shareholders in VocaLink, with a 21.4 per cent stake, and said it will see a profits boost of about £150m initially.
Barclays confirmed it is set to gain up to £133m from the sale for its 15.2 per cent stake, while the Co-operative Bank will get up to £28.3m for its 3.3 per cent holding. Following the deal, the banks will retain a 7.6 per cent stake in VocaLink for at least three years.
Ajay Banga, president and chief executive of Mastercard, said: “We’re excited about the opportunity to play a bigger role in payments in the UK, a very strategic market for us. VocaLink is a unique company with outstanding technology, assets and people.”
David Yates, chief executive of VocaLink, who will join the Mastercard management committee after the deal, said: “We will continue to focus on ensuring that the UK systems perform seamlessly.
“At the same time, we’ll invest in further innovation to power competitive payments solutions for consumers and businesses around the globe.”