Researchers suggest £4m will be generated in additional sales of beer, confectionery and food.
Another £2.8m could be spent at pubs and fan zones during matches, including on transport and fast food.
The survey suggests £2.5m will be spent on NI home and away shirts and other official merchandise.
Andrew Webb, senior advisor at the Ulster University's economic policy centre, said: "The European Championship finals is a significant sporting event for Northern Ireland but with the added benefit of not having many of the associated costs that come with actually hosting the event.
"The buzz surrounding the tournament will bring more people to pubs and fan zones to watch the matches as well as see them organise get-togethers at home.
"As retailers benefit from the additional expenditure that comes from this, there is an increase in demand on their suppliers and so on down the supply chain."
Researchers categorised the impact in several ways
Mr Webb said the figure of £8.5m was "most likely conservative".
"There are, of course, a range of wider additional benefits which we can't quantify such as extra advertising and publicity for Northern Ireland as a result of the Euro 2016 qualification as well as sponsorship deals and television rights packages that may come later, with a higher profile team.
"So it is likely that the total economic benefit would be slightly higher than we have estimated."
The Northern Ireland football team secured their place at the Euro 2016 finals last October after beating Greece 3-1.
Michael O'Neill's squad is due to play against Poland in Nice on Sunday.
The Northern Ireland economy could benefit by more than £8.5m due to NI's qualification in Euro 2016, according to an Ulster University survey.