National Grid has signed a joint venture agreement with transmission system operator Elia for the 1GW Nemo link interconnector between the UK and Belgium.
The line will run 140km between Richborough on the Kent coast and Herdersbrug, near Zeebrugge, with undersea and underground cables.
Energy will flow in both directions between the two countries. The link is expected to start commercial operation in 2019.
Nemo Link will provide a third interconnector between UK and Europe. A 2GW link to France and 1GMW link to the Netherlands are currently in operation.
The parties will announce contracts for the construction of the converter stations and cable laying after finalizing suitable deals.
Engineering design work and site preparation is expected to start later in 2015.
UK Energy and Climate Change Secretary Ed Davey said: "Better electricity links to our neighbours help to guarantee our energy security at the lowest possible cost to billpayers and mean we can use renewable electricity more effectively, allowing excess generation to be exported.
"This new interconnector will increase the amount of capacity available through interconnectors by 25%.
"Nemo is not only an important interconnector in its own right, it also demonstrates that the new cap and floor regime can help support new investment while protecting consumers."
The Belgian grid is at the crossroads between electricity markets in Western and Eastern Europe. It currently has the capacity to import 3500MW of capacity with plans for a further 1000MW interconnection with Germany.