The deal, for which financial terms have not been disclosed, will see Fortis take over Dominet's established network of 152 Polish retail branches, along with a workforce of over 800 employees.
According to the bank, Dominet has a strong business in car financing, with relationships with over 2,000 car dealers across the country.
"International growth of our Retail Banking activities is a pillar of Fortis's strategy, and therefore the acquisition of Dominet represents a step forward that will help us to expand our activities in the interesting Polish market," commented Jos Clijsters, chief executive of Fortis Retail Banking
"Dominet will be part of the Fortis structure and I trust our enhanced offering in Poland will benefit both existing and future customers."
Fortis is currently among the 20 largest financial institutions in Europe in terms of market capitalization, with a presence currently in over 50 countries.