Mr O'Mahoney, who was the bank's chief operating officer, retired a year ago after failing to secure the chief executive's post.
The bank's annual report for 2005 reveals that Mr O'Mahoney was paid €3.65m when he left. Anglo Irish also topped up his personal pension fund to the tune of €250,000.
Anglo's remuneration committee voted to make the payment to Mr O'Mahoney given the length of time he was with the bank and his contribution to building up the business.
Along with former chief executive (and now chairman) Sean FitzPatrick, Mr O'Mahoney was the chief architect of Anglo's success. He had been favourite to take on Mr FitzPatrick's role, but was passed over in favour of 39-year-old David Drumm.
Since retiring from Anglo, Mr O'Mahoney has set up International Securities Trading Corporation (ISTC) to invest in regulated bank capital and other capital market issues.
The Anglo annual report shows that Mr Drumm was paid a total of €2.3m in the year to end September. His remuneration package consisted of a basic salary of €663,000, a bonus of €1.5m and other benefits of €191,000.
John Rowan, who runs Anglo Irish's British business, took home €1.62m which was €100,000 more than in 2004. His pay included a cool €1m performance bonus.
Group finance director Willie McAteer netted an extra €132,000 to bring his total pay packet to €1.54m.
Tom Browne, who heads the bank's wealth management division, picked up €1.52m, which also included bonuses worth €1m
Sean FitzPatrick was paid just over €1m, according to the report.
Some €764,000 was shared by the company's 10 non-executive directors. These include Dublin Airport Authority chairman Gary McGann, who received €65,000 in fees. RTÉ Authority chairman Fintan Drury also picked up €65,000, as did Paddy Wright, the former Smurfit boss.
Lar Bradshaw, the chairman of the Dublin Docklands Development Authority, who joined the board in January received €63,000 in fees, while Greencore chairman Ned Sullivan was paid €75,000 for the part-time non-executive role.
Overall, payment to the company's directors totalled €9.04m in 2004/2005, down from €9.1m over the previous 12 months.
But the board are by far the highest paid directors of a publicly-quoted Irish company.
Anglo Irish Bank made pre-tax profits of €685m this year, 35% more than in 2003/2004.