Financial results from IAG show that Aer Lingus made an operating profit of €45m since it joined the airline group in August.
The parent company's operating profit was €1.2bn in the three months to the end of September, excluding Aer Lingus profits.
That was an increase of €350m on the same period last year.
IAG chief executive Willie Walsh described Aer Lingus as “a great asset”.
He said: "Aer Lingus made an operating profit of €45 million since it joined IAG on August 18th. While the airline’s profitability is seasonal, Aer Lingus is cost-effective and provides a natural gateway to build our business between Europe and North America. It’s a great asset for the group."