Facilities include pitches, medical equipment, coaches and backroom personnel.
Funding has included £1.5m of National Lottery funding from the Sports Council for Wales, and £1m of additional WRU support to complete the project.
It will also house the newly-formed WRU national academy, while the World Cup-winning Wales sevens group is based there, together with coach Warren Gatland's senior squad.
There are three outdoor full-size pitches, along with additional training zones where players can focus on scrummage and lineout technique and performance.
One of the three pitches has an all-weather surface and is fully floodlit.
Welsh First Minister Rhodri Morgan, who performed the opening ceremony, said: "This state-of-the-art facility will give our elite national squads the best possible opportunity to gain an edge and win those games where an extra two or three percent is the difference between success and defeat."
And Gatland added: "We have now created an inspirational working environment where the coaches and players can focus on development and match preparation.
"One of our core values is that each player holds a responsibility to the Welsh jersey, and if we ask them to give their all for that we have a duty to help them as much, and as professionally, as we can.
"We are already enjoying the benefits of working together under one roof and at one base, so we all get plenty of opportunity to engage and share ideas.
"We know the raw talent exists at all levels in Wales, and the National Centre of Excellence is the right place to nurture and develop that."