A total of 350 new jobs are to be created at Ulster Bank's Direct Customer Contact Centre in Danesfort, Belfast.
The new staff will mainly be working on RBS and NatWest customer accounts and the centre will continue to support calls from Ulster Bank customers across Ireland.
IBOA general secretary Larry Broderick said that a number of factors contributed to the decision by RBS to locate the work in Belfast.
"The crucial part of the equation has been the consistently high level of performance of our members in Danesfort - which has been recognised by independent industry experts in both Ireland and the UK," he said.
He also acknowledged the efforts made by Ulster Bank to "lobby" RBS to make this additional commitment to the business in Ireland.
The bank already employs 250 people at the centre in Belfast and said it would invest a further £300,000 (€407,000) for additional office space to accommodate the new staff.