Twelve teams will take part in the new European club league when it kicks off in October.
Leading clubs from Wales, France, Romania and Italy will compete alongside Ireland's major provincial sides in the inaugural tournament, which will run until December. England and Scotland, who were unable to change their fixtures for the forthcoming season, will complete the line-up next year when it will become a 16-team championship.
"I'm delighted we are there at last after nine months of hard work," the Welsh chairman, Vernon Pugh, said. "It could have been earlier if some clubs hadn't muddied the waters, but it will be a good thing for the European club game.
"We have got two major international companies interested in sponsoring the competition and a decision on that, and a number of other matters, will be taken by the end of July."
Wales have already invited the Heineken League champions, Cardiff, the runners-up, Pontypridd, and the cup winners, Swansea, to take part, while the French have entered their cup winners and two top league clubs.
The Irish, concerned their club sides would not be strong enough to compete, have asked three provincial sides to enter - with champions Munster, Leinster and Ulster likely to be chosen.
Michael Lynagh's Treviso, Wayne Shelford's Rome and Diego Dominguez's Milan sides are competing for the two places likely to be granted to the fast-developing Italians, while Romania will put forward their top club side.
Each team in the championship, which will contain four pools, will be guaranteed one home and one away match, with gate receipts being retained by the hosts. The winners of each group will go forward to the semi-finals, limiting the number of games any team will play to four.
"That should be no great burden on the players, but will give them a taste of standards and competition above their current domestic levels," Pugh added.
The Scottish reacted favourably to the European Championship but would be loath to field club sides.
Scotland's director of rugby Jim Telfer said: "Anything that gives our top players the chance to play at a higher level can only be a bonus. If Scotland become involved then we would want our districts to participate.
"The Italians and the Welsh would enter top club sides like Rovigo or Cardiff but we see the way forward as districts taking part."
Telfer added: "We would have to take the clubs in Scotland along with us in any decision-making. They, after all, will supply the players for any district side."
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