South Africa's former Super Rugby sides will be introduced to the Pro14 teams from April 2021 in a new Rainbow Cup competition.
Bulls, Stormers, Sharks and Lions will participate, before potentially joining a new league with sides from Ireland, Italy, Scotland and Wales from 2021-22 on a permanent basis.
Sixteen teams are scheduled to compete in the Rainbow Cup.
The Pro14 league season will end early, with the final scheduled for 27 March.
Talks to include the four South African teams officially began in September after SA Rugby voted in favour of the move following New Zealand's plans to launch their own trans-Tasman competition with Australia.
Cheetahs and Southern Kings joined the then Pro12 in 2017 to form an expanded Pro14 competition but their involvement has now ended.
Kings have ceased operations, while Cheetahs have retained their professional franchise status with SA Rugby and are to explore other opportunities to play in international competition.
Finishing the season
The decision to halt the Pro14 early has been made by tournament bosses who are keen to support South African rugby ahead of the 2021 British and Irish Lions tour, as they face the prospect of no international club fixtures to prepare for the Test series against Warren Gatland's side.
The South African sides will be able to include World Cup-winning Springboks Siya Kolisi, Pieter Steph du Toit, Duane Vermeulen, Elton Jantjies and Makazole Mapimipi.
This season's Pro14 tournament has had 12 sides competing in the league. They had been due to play each other once by the middle of January in the opening 11 rounds, although a number of games have been postponed because of Covid-19.
The competition will now be reduced to 16 rounds, with the final five games happening between 20 February and 20 March - a period which includes three Six Nations weekends.
A final on 27 March will be held between the two conference leaders, with the team with the most match points having home advantage.
The top-ranked teams from each conference will qualify for the 2021-22 Heineken Champions Cup.
The exact number of sides that qualify for Europe's top club tournament will be confirmed once tournament organiser European Professional Club Rugby (EPCR) announces its competition formats for next season, with a Pro14 play-off still being considered if required.
How will the Rainbow Cup work?
The Rainbow Cup will begin on 17 April, 2021 with the competition split into two pools of eight teams and 57 games scheduled.
A group tournament will run for seven rounds before a final on 19 June between the pool winners.
Each pool will consist of two sides from Wales, Ireland and South Africa and one from Scotland and Italy.
No details have been provided yet about the 2021-22 season with discussions ongoing but this cup competition is considered a step towards a league tournament involving the four South African sides.
"At a time where our sport has faced its greatest challenge, we have promising news about the future of our tournament and the strengthening of our partnership with South African rugby," said Pro14 CEO Martin Anayi.
"As our teams and unions have worked relentlessly to keep our sport alive, we have been tasked by our shareholders to map out a future that provides greater certainty and allows for a more harmonious calendar between club and country.
"It was vital we worked with all parties to ensure our current 12 teams had a clear road towards European qualification ahead of introducing any new teams.
"With a British and Irish Lions tour to come, it is hard to think of anything better to whet the appetite than the best players from the Celtic regions competing against World Cup-winning Springboks in the Guinness Pro14 Rainbow Cup."
SA Rugby chief executive Jurie Roux added: "The inclusion of South Africa's 'Super' teams in the Rainbow Cup is a once-in-a-generation, watershed moment for South African rugby.
"After so much turmoil and uncertainty in 2020, the prospect of a return to top-flight international domestic competition is one to which we all can all look forward with real excitement."
Will teams be able to travel?
The Rainbow Cup games are scheduled to be held in Europe and South Africa. The tournament has been announced at a time when international travel restrictions are at their most stringent because of the Covid-19 pandemic.
Between April and June, each South African team will be required to play three away games in Europe and these fixtures will occur in blocks, meaning one trip of two-and-a-half weeks.
European teams will all play one away game in South Africa. So the viability of the competition will be the main concern for organisers.
On the issue of players protecting their Covid-19 bubbles while travelling across hemispheres, Pro14 rugby said: "We are in continuous discussion about Covid-19 protocols with our medical advisory group, made up of our chief medical officers across the Irish, Italian, Scottish, South African and Welsh rugby unions.
"The information and resources available to protect our teams is always improving and the group will continue to provide direction based on the latest guidance available at the time."