Qatar Airways will receive £1m from the Welsh Government to market Wales as a destination around the world.
It initially refused to reveal the cost, claiming it would compromise the economic interests of the country.
The airline will also contribute £1m to the two-year partnership, which has an option to extend for a further two years for another £1m each.
First Minister Carwyn Jones previously described the deal as a "huge boost" for Wales.
The Welsh Government had originally said the deal's significance could not be "underestimated", and the value and structure was commercially sensitive.
Opposition politicians had criticised it for not releasing the information, but the Welsh Government had said it strived "to be as open and transparent as possible".
The Welsh Government said it had made a payment to the airline in the financial year ending March 2018, and another payment will be made in the second year.
The contract will be monitored by the Welsh Government and Qatar Airways.
The Welsh Conservatives' economy spokesman Russell George AM said the news that £1m of public money was spent on the marketing deal raised "serious questions".
"I am hugely ambitious for Cardiff International Airport and want it to thrive through the securing of new commercial partners like Qatar Airways," he said.
"However, when taxpayer money is being used to support a deal, transparency and openness on the part of the Welsh Government is essential."
A spokeswoman for the Welsh Government said the marketing partnership was put in place to make the most of the Qatar Airways air link and had been widely welcomed as an "important mechanism for increasing Wales' visibility as both a holiday and business destination in key markets".
"Activity includes consumer marketing as well as travel trade engagement and press and media activity and a global campaign on Qatar Airways' owned channels. The partnership has also enabled Visit Wales' first direct consumer marketing activity in key Australian cities," she added.
The service was launched in May and started running daily from the middle of June.
Last week, Qatar Airways chief executive Akbar al-Baker told The Independent that the Cardiff to Doha route was not performing as expected in terms of passenger sales.
However, he said their freight service had performed well.
Cardiff Airport said all routes take time to mature and that more than 1,500 passengers had flown on the route in the previous week, out of 1,750 seats potentially available.