The agency team, led by managing partner Rory Godson, has been helping the bank’s CEO John Hourican communicate its turnaround story internationally.
Hourican was appointed last October in the wake of a humiliating bailout whereby the commercial bank’s depositors were forced to become shareholders.
The bank took a step back to normality by bringing in billionaire Wilbur Ross alongside some additional financial institutions as shareholders last week in a €1bn (£792m) capital raising.
Hourican, who previously worked with Powerscourt while at RBS, appointed the agency on a retainer without a pitch in April.
The agency team, which includes Karen Le Cannu and Justin Griffiths, was also involved in the restructuring of the Bank of Ireland, in which Ross also invested.
Hourican said: "Powerscourt has a crucial role in communicating our strategy and we are benefitting from its first-class media relations advice and execution ability."
Separately, FTI Consulting is understood to still be working for the government of Cyprus, which brought the agency in to handle international communications in early 2013 as it fought to secure a bailout from the European Union.