The Green Army have spent more than €200m supporting the Ireland team in France, while a further €100m has been generated for the Irish economy by fans watching games at home.
On average, supporters who travelled to France have spent more than €2,000 each on travel, accommodation, food and drink.
This figure could rise when families are taken into consideration, along with trips to Disneyland in Paris, vineyards in Bordeaux and other excursions over the past two weeks.
Economist Jim Power said this indicates a renewed confidence in Ireland's economy.
"A lot fewer people travelled to the Championships in Poland four years ago because it was more financially difficult for people to do so than today," said Mr Power.
"To see that many people travel overseas is a key indicator that the economy is better, personal finances are better and, crucially, that they have more confidence in the future. Some obviously would have borrowed from credit unions and banks and they are confident they can pay it back."
The €200m spend came as 20,000 fans travelled to all three venues and attended all three matches since June 13.
However, tens of thousands more travelled to one or two venues for matches - while thousands of others went to Paris, Bordeaux or Lille without going to the games.
Irish supporters groups estimated that even the most cost-conscious fans faced a bill of between €1,500 to €2,000 if they stayed for a two-week break.
However, other fans have spent more than €5,000 by opting for luxury hotels, buying black-market tickets and eating in fine restaurants.
"I think there will be fans who spent a lot more and some spending a little bit less but on average 100,000 people spending that amount of money, €200m is a very realistic assessment of the amount of money being spent," said Mr Power.
"That is a direct loss to the Irish economy but many of those people would have gone overseas anyway and went to the tournament rather than go to Spain or somewhere else."
Ireland's qualification also boosted business at home as fans flock to pubs and restaurants to watch the matches.