The Pro14 has agreed a deal in principle to sell a 27% stake of the league to private equity firm CVC Capital Partners.
The deal will result in a cash boost of almost £120m to the league owned by the Irish, Scottish and Welsh Rugby Unions.
Each union would have a cash injection of around £35m, with sides from South Africa and Italy also benefitting.
CVC will buy a minority shareholding after agreeing a similar deal with English clubs.
Pro14 bosses have been in long-term discussions with CVC after the firm bought a stake in the Premiership in December 2018, a deal worth more than £200m for a 27% stake.
The Six Nations is already in "an exclusive period of negotiation" with CVC to sell a stake in the game's oldest championship.
CVC would take over the commercialisation of the Pro14 from Celtic Rugby DAC, which runs the league, particularly in the areas of sponsorship and broadcasting.
There has been talk about developing the league from the five countries that already play in the tournament, with the north American market being targeted.
The deal is yet to be officially ratified and approved but a Celtic Rugby DAC statement confirmed CVC's interest.
The statement read: "Celtic Rugby DAC and its shareholders can confirm a request has been filed to the Irish Competition and Consumer Protection Commission for Merger and Acquisition clearance by CVC Capital Partners.
"The request has been made in relation to a potential transaction involving Celtic Rugby DAC and CVC Capital Partners.
"Both parties are involved in advanced discussions and until those talks have been finalised there will be no further comment."
News of the deal was also revealed at the Welsh Rugby Union's annual general meeting at the Principality Stadium in Cardiff on Sunday.
WRU chairman Gareth Davies says private equity would be welcomed: "It is an interesting departure and development.
"It is commonly known that the Pro14 has been in discussion with CVC and it looks like that could be moving forward.
"There are still i's to be dotted and t's to be crossed but that is moving on. That will be an influx of money into Ireland. Scotland and Wales and that is well received.
"Discussions are ongoing and hopefully there will be some extra funds in our coffers. It will come into the Union first of all and we are in discussions with the (Welsh) regions and they will benefit as with others.
"Looking at the Pro14 it is an easier entity to offer a share. In England they have gone directly to the clubs because they are the ones negotiating."
Davies says he is not concerned with losing control of the league, with the Pro14 maintaining a majority 73% stake.
"The rugby element will still be controlled by the Unions and professional team," said Davies.
"Rugby is not always good at working together because there are lots of areas of self-interest.
"It probably needs an external partner to knock heads and to more commercialise what is regarded as an underexploited sport."