Details of the new long-term arrangement were agreed in discussions between the WRU and the Welsh Rugby Players Association held over the past months.
The contract covers arrangements for players' medical cover, insurance and general welfare throughout the year.
The agreement forms the basis of a complete support system for the players during and after their rugby careers.
WRU Group Chief Executive Roger Lewis said: "We are delighted to have been able to achieve such a breakthrough agreement which is good for the players themselves and for the future of Welsh rugby.
"By agreeing to a structure which will be in place for the next four years we can focus on long term planning and the sustainability and success of our game.
"We have achieved this successful outcome in our talks so quickly because we all had the best interests of the players and the game at heart and the players, in turn, have been open and receptive to a new relationship with the Union.
"The agreement will allow us to reward success and enable the players to benefit from the incredible effort they put in for their nation here at the Millennium Stadium and for Wales as they travel around the globe.
"We all structured our thinking to ensure the players get what they deserve and their continued success will continue to reap benefits which will help develop the game from the elite level to the grass roots in Wales.
"A winning Wales generates the funding to fuel the game throughout Wales."
WRPA Chief Executive, Richard Harry said: "I am delighted we have reached such a successful and positive conclusion.
"The negotiations with the WRU were conducted positively and professionally and have resulted in an agreement that reflects the huge effort that the players put in to their time with Team Wales, whilst providing rewards for success.
"Our discussions have also allowed us to consider the game in a wider context and I am looking forward to working with Roger Lewis and his team on creating the best possible environment for our players in Wales."