The route came into operation on January 14th last year as part of ten new flights launched from the Northern Irish capital in December 2007.
Commenting on the popularity of the flight, Enda Corneille, Aer Lingus’ corporate affairs director, said that Belfast was the carrier’s first base outside of the Irish Republic and that it continued to be successful.
"In our first year of operations we took more than 750,000 bookings, that was 50 percent ahead of our target and we are well on our way to our millionth booking," he said.
Mr Corneille added that that the airline was proving popular among the Northern Irish public due to its cheap fares.
As well as London Heathrow, Aer Lingus flies to Paris, Barcelona, Rome, Munich, Milan, Amsterdam, Faro, Lanzarote and Malaga from Belfast, with a flight to Tenerife being launched from the airport in September.
The airline confirmed earlier this month that it had met representatives from Ryanair to discuss its possible takeover.