Mr Quinn's first business venture in 1973 was a small gravel pit
Sean Quinn and his family have bought a 15% stake in the Anglo Irish Bank worth about 500m euros.
They said they regard it as a long-term investment "with significant opportunity for capital growth".
It is thought to be a private purchase outside of the Fermanagh businessman's range of company interests. These interests include insurance, concrete and glass manufacturing, pubs, hotels and a power station in County Louth.
Last year, the Quinn Group made profits of 433m euros - an increase of nearly a third on 2006. It also bought the health insurer BUPA Ireland.
Mr Quinn and his wife and children own the companies outright and are believed to have amassed a personal fortune of nearly 4bn euros.
The Quinn Group employs more than 5,000 people throughout the world and have recently expanded into India and Russia.
Mr Quinn began in business in 1973 at a small gravel pit on the family farm in Derrylin, County Fermanagh.