The two Polish banks in which AIB has a majority stake have completed their legal merger.
The new entity, formed by the merger of Bank Zachodni and WBK, will be known as Bank Zachodni WBK, with AIB holding a 70.5% stake.
The merger creates Poland's fifth largest bank with a combined branch network of 419. The bank will have its head offices in Wroclaw.
"Bank Zachodni WBK stakeholders can now look forward to benfitting from the combined scale, strong uniform product offering and focused quality service to customers," said Gerry Byrne, the new head of AIB's Polish division.
AIB shares closed up 18 cents at 12.55 euros, as the company engaged in talks to sell its interest in Singapore bank, Keppel Capital Holdings.