The move follows a 12-way pitch revealed in PRWeek (12 November 2004), eventually shortlisted to six firms thought to have included Brunswick, Citigate Dewe Rogerson and Maitland.
Powerscourt's appointment ends a two-year relationship between Bank of Ireland and Maitland.
Powerscourt co-founder Rory Godson and director Victoria Brough are leading the account, which will be reviewed in six months' time.
Bank of Ireland is revamping its PR following the restructuring of its UK operations and ventures, from which the bank derives around 30 per cent of its revenue and where it has a secondary listing on the London Stock Exchange.
The Bank has expanded its financial services offering through a joint venture with the Royal Mail, selling loans and motor insurance over the counter of 16,000 post offices.