A biennial competition featuring all 10 teams from the Six Nations and Rugby Championship is set to start in 2026.
It will be played in the existing July and November Test windows in alternate years, outside of British and Irish Lions tours and the World Cup.
Two more unions will be invited to join, with plans to introduce promotion and relegation from 2030 via a second-tier competition run by World Rugby.
Organisers say the move will “drive growth and long-term sustainability”.
The tournament will feature England, Scotland, Wales, Ireland, France and Italy from the Six Nations and Rugby Championship teams South Africa, New Zealand, Australia and Argentina – collectively known as Sanzaar.
Six Nations and Sanzaar organisers said there would be a “transparent selection process” to choose two more teams from the southern hemisphere to ensure there are six from each.
Although no format has been confirmed, reports suggest teams from the north would travel south for three Tests in July and then host three games in November.
The Six Nations would remain in its current February-March position on the calendar and the Rugby Championship would still be played in August-September.
“The creation of the new competition has been a collective process from the sport, including World Rugby, unions, key leagues, competitions, and crucially, the International Rugby Players (IRP),” said the Six Nations and Sanzaar.
“Establishing the two competitions will pave the way for promotion and relegation matches, contributing towards a valuable pathway for teams, and will support ambitions to sustain and grow the global game.
“The impact this will have on the game will be to drive its growth and long-term sustainability.
“This runs alongside the work being done to add greater clarity and balance to the club and international calendar; a process Six Nations Rugby and Sanzaar remain committed to help deliver.”
Rugby leaders met in London this week, when it was announced that a decision would be made on the sport’s future global calendar by the World Rugby Council in October.
Representatives from World Rugby, the British and Irish Lions, the Six Nations, and the Rugby Championship, along with stakeholders from IRP, the unions and professional leagues all attended.
The IRP tweeted its views on the talks, saying: “Any global season must have opportunities for emerging nations and must put player welfare first and foremost.”
The players’ body has also called on World Rugby to standardise player rest periods and introduce a maximum match quota for all players worldwide.
