The operators of Waterford Airport say the €5m State investment in the facility will be paid back in less than four years.
Chairperson of the airport Board Dan Browne was speaking after Minister of Transport Shane Ross authorised the grant against the advice of Government officials.
Mr Ross has told RTÉ News the concerns of the Department of Public Expenditure had been addressed, and although the investment was risky, it was being shared with the private sector.
The airport has been without commercial flights since a Waterford-Luton route ended in June 2016.
A handful of private aircraft land at the airport every week and it is a base for the coastguard rescue helicopter.
Speaking to RTÉ News, Mr Browne said that a PWC report into the viability of the airport suggested investment could lead to the employment of 100 people and generate an annual income of €4.5m.
Mr Browne said the State's investment would be returned within four years.
He said: "We had to work hard to make the case. Government are going to do quite well out of this.
"If we get 5,000 overseas visitors the State will make €730,000 every year. There is also 100 direct and indirect jobs.
"The Government will be getting their returns back very early on."
Mr Browne said the majority of flights in an expanded Waterford Airport would service London.
"When the airport started first it did very well in flights to London and we would still see that as being the principal part of our business.
"We did have in the past tourist-type flights, so the locals will be particularly interested if we can bring those back," he added.
Mr Browne said the length of the runway was not sufficient to deal with the bigger aircraft.
"It's about making a serious case to develop the region," he said.
Speaking in Abbotstown in Dublin today, the Taoiseach said he supported the decision to give €5m to Waterford Airport.
He said it has to stay open as it is a Coastguard base even though it has not had commercial flights in a couple of years.
He said the investment along with a further €7m from private investors and three local authorities has the potential to make the airport viable and profitable again.
Elsewhere, Minister of State for Training and Skills John Halligan said the €5m investment from the Government was "a small amount".
Speaking on RTÉ's Today with Sean O'Rourke, Mr Halligan said the southeast should have the same infrastructural opportunities as everywhere else in Ireland.
The Waterford TD asked why the region should be excluded when every other region across Ireland has an airport.
Mr Halligan said there would be plenty of use out of it and there are three councils and a number of big companies and individuals ready to invest in the airport, amounting to around €7m, of which €5m was private investment.
He said Mr Ross had met representative of businesses in Waterford, as well as a number of politicians, who all backed the move.
Mr Halligan said he has always advocated for a runway extension at Waterford Airport, and the further development of the economy in the southeast, but the problem over the years for Waterford is that it is impossible to get "prop" planes to land there.
He said the airport "was viable and hundreds of thousands of people were flying from there when you were able to land prop planes down through the years".
Mr Halligan indicated it would be a case of "build it and they will come", adding that the business would be there once you have the jets.