The development, due for completion in autumn 2014, will add a new 250sqm gallery space, as well as a restaurant on the second floor of the Euston Road venue.
The investment will also create a spiral staircase as the focal point for the galleries and see the 200-capacity Medicine Now Gallery take centre stage for private hire evening receptions.
The venue will remain open throughout the development, continuing to host events in its six existing spaces, which include the Henry Wellcome Auditorium for up to 154 delegates.
Conference centre manager Rachel Cordier said: "We are delighted that the plans are now underway.
"This substantial investment in our product and on-going development will further strengthen our market presence and help us approach new customers and market sectors."
Pavilion Publishing, the British Psychological Society and the National Institute for Health Research are among recent clients to have held events at the venue.