The Celtic League will go ahead as planned next season after the Scottish, Irish and Welsh rugby unions agreed a four-year deal in London on Friday.
Wales were expelled from the competition on 31 May for joining a new Anglo-Welsh Cup.
But a compromise has been found to accommodate Welsh teams playing in both competitions in 2005-06.
The unions also agreed to meet at the end of the season to discuss bringing Italian teams into the Celtic League.
The Anglo-Welsh Cup was designed to replace the Powergen Cup in the English domestic calendar but its creation required Welsh clubs being free of Celtic League fixtures for five weekends of the season.
This was objected to by Scotland and Ireland but the Welsh Rugby Union insisted they remained full committed to the Celtic League and agreement was reached at the meeting at Heathrow Airport.
A statement read: "As a consequence of a very positive and productive meeting in London today the Celtic League Association confirm that the three unions have reached agreement to accommodate the proposed Anglo-Welsh cup competition in the 2005-06 season."
The expulsion of the Welsh regions had left them facing the possibility of just nine guaranteed fixtures per season.
But the WRU believed a solution could be found by arranging fixtures in a certain way and having Welsh clubs play in midweek.
The Celtic League will start in September with each club playing 20 games.