The expansion work will add 4,000m2 of flexible space to Belfast Waterfront, which is Northern Ireland’s only purpose-built conference centre.
More than £1bn has been spent over the past ten years to transform the city.
Belfast was recently named the UK’s Best Conference and Incentive City Destination by C&IT magazine.
Jennifer Patterson, revenue and business generation manager at Belfast Waterfront Conference and Exhibition Centre, said: "We’re looking forward to seeing our architectural plans become a reality as construction on the new extension gets underway.
"Doubling the size of our facility is a further sign of our commitment to strengthening the city’s capabilities to attract many more major conferences and events, as well as bring £39m to the local economy annually."