The agreement was signed at a summit in Paris.
The project, which would connect the cities of Lyon in France and Turin in Italy, includes the construction of a 57-kilometre tunnel for an estimated cost over 8 billion euros (USD 7 billion).
The line would not open before 2028.
The European Union authorities promised to finance 40 per cent of the project.
Ultimately the line could also be adapted for a high-speed passenger trains.