Starting March 31, there will be four flights a week from Terminal 5.
The service will increase the number of flights between London and Japan offered by BA and joint partner Japan Airlines to 32 a week.
Operated by a Boeing 787-8 Dreamliner, special return fares start from £599 in World Traveller, £999 in World Traveller Plus, and £2499 in Club World.
British Airways flies direct from Belfast City Airport to Heathrow, making Osaka and the rest of the world more accessible than ever.