Ulster Bank chief executive Jim Brown said he was turning down this year's annual bonus after a computer meltdown left thousands of customers without access to cash.
He pledged an independent inquiry into the IT collapse last month which affected customers across Ireland and said nobody would be left out of pocket. Details of a compensation package will be announced within days.
Despite insisting hours earlier he would not make a decision until his bonus was reviewed at the end of the year, he said last night he would not be taking it.
He said: "Everyone at Ulster Bank is completely focused on putting things right for our customers.
"I don't want there to be any doubt that this is also my personal priority.
"I am personally committed to re-earning the trust of our customers.
"I have therefore informed the Ulster Bank board that I do not wish to be considered for an annual bonus award for 2012."
It followed calls from politicians north and south of the border to turn down his bonus this year as a goodwill gesture.
The bank initially estimated that about 100,000 customers across the country had been affected by the error, some with limited or no access to their funds at all.
Mr Brown told an Oireachtas (Irish Parliament) committee the figure is much higher than originally believed and that at least half of Ireland's 1.1 million customer base has suffered.
The bank has an estimated 1.8 million customer base across both the Republic and Northern Ireland.
The banking boss unreservedly apologised to customers and said the situation was unacceptable, but he ignored calls from Sinn Fein TD Pearse Doherty to reconsider his position.
"My focus right now is getting the bank back to normal as quickly as possible," said Mr Brown.
He also refused to reveal his salary for this year to cross-party politicians in Dublin, adding that the figures would be disclosed in the bank's annual report when published in October.
Earlier, at a Stormont committee in Belfast, Mr Brown said details of compensation payments to customers in financial difficulties because of computer problems at the bank would be ready within days.
He also promised an independent investigation into the IT failure, which left many customers with unpaid bills.
"It is unacceptable and our customers should expect better from us," he said.
"No customer will be left out of pocket as a result of this incident."
The system for processing payments - which had worked properly for 25 years - broke down on the evening of June 19 when maintenance on the computer system interfered with the processing of payments for the day's trading, he said.
That meant that the next day many customers' balances had not been updated.
By the time the technical problem was resolved there was a backlog of payments pending - including the updating of accounts, direct debit payments, benefits and mortgages.
Chris Sullivan, an executive at Ulster Bank's parent company, the Royal Bank of Scotland, said the bank still did not know exactly what had caused the IT problem.
He said it would be addressed by a forensic, open and transparent independent review into what went wrong, which would be shared with regulators, customers and the rest of the industry.
He also defended the banking group as a whole, claiming that no priority had been given to UK-based RBS and NatWest over Ulster Bank.
Technical failures at the former two have already been addressed and resolved, while Ulster Bank customers in the Republic and Northern Ireland are still being affected.
"There is no priority given because of size or geographic nature," said Mr Sullivan.
He said progress at Ulster Bank had lagged behind due to IT reasons alone.
Meanwhile, Ireland's prime minister, Enda Kenny, criticised the lack of service for customers of Ulster Bank.
"It's not acceptable in this day and age that people should have to put up with the fears and the anxieties - and the loss of service - that's been there," he told Galway Bay FM.