The group run by Willie Walsh formally took over Aer Lingus last August.
Since the acquisition, Aer Lingus has contributed €622m in revenues and €35m before exceptional costs in operating profit to the group.
The Aer Lingus yield — the amount of money earned per seat — had improved, driven by “a strong performance across the North Atlantic”, IAG said.
IAG is already renewing the fleet of its Iberia arm with Airbus A350 and A330 long-haul planes over the next five years.
Aer Lingus will also get two A330s and IAG is converting options for the re-engined A320neo model to be allocated between its carriers later.
It is establishing itself as Europe’s most profitable airline as Air France-KLM and Lufthansa grapple with unions over cost cuts.
Aer Lingus will provide a full year of earnings in 2016, while a potentially lucrative joint venture deal with Latam Airlines could spur profit from next year.
Mr Walsh said he is in detailed discussions with potential suppliers of used Boeing Co 777-300ER aircraft and is continuing to look at leasing a batch of A380 super jumbos. Group operating profit increased to €2.34bn from €1.39bn.
“It’s undoubtedly been a good year, but it’s also been challenging with extreme volatility in the currency and fuel markets,” said Mr Walsh.
“Overall, North America and Europe were the strongest markets.”
Full-year earnings were in line with IAG’s forecast for adjusted operating profit in the range of €2.25bn to €2.3bn.