Work on a new £83.7m convention centre at the Celtic Manor hotel site in Newport will start in March.
A funding package for the International Convention Centre Wales has been agreed by the hotel, the Welsh Government and NatWest.
The venue, projected to open in June 2019, will accommodate up to 5,000 delegates in a 1,500-seater auditorium and separate exhibition hall.
It would be the largest centre of its kind in Wales and south west England.
Excavation work has already begun on land next to the hotel and existing convention centre, overlooking the Coldra M4 junction 24 roundabout.
A 2,500 sq m plaza will be constructed as a welcome and additional exhibition area and 700 parking spaces will be built underneath the centre.
A joint venture company will construct and manage the centre as an equal partnership between the Celtic Manor and the Welsh Government.
Celtic Manor Resort chair Sir Terry Matthews said: "This International Convention Centre has been many years in the planning and I am delighted that we are now in a position to build and deliver this facility that will be such an asset to Wales.
"In the past, we've been forced to turn away hundreds of millions of pounds of business because we did not have the capacity to hold the largest conferences. Not any longer."
Economy and Infrastructure Secretary Ken Skates AM added: "This will be a major asset for Wales, enabling us to compete with any venue in the UK and indeed Europe to attract and host key events that make a huge contribution to the economy."