WRU chief executive Abi Tierney says professional rugby needed to be kept in Cardiff.
“Our first concerns are with the players, staff and supporters,” said Tierney.
“They can be assured professional rugby will continue at Cardiff Arms Park.
“We have been keeping in close contact with the Cardiff Rugby Board for several months once they became aware of the risks to anticipated shareholder funding not being available.
“As a result, the WRU has been able to move quickly to provide support for Cardiff.”
The WRU say Cardiff is the largest of the four professional clubs in Wales, with a regional population containing more clubs and schools than any other.
“It is unthinkable for us to allow the demise of professional rugby in the Welsh capital,” said Tierney.
“There has been no hesitation for the WRU as we quickly moved to pull a rescue package together.”
Cardiff Rugby chair Alun Jones says “the priority has been securing our staff, the future of the club and the rugby pathway in the capital city and wider region”.
“We are incredibly grateful to the Welsh Rugby Union for securing our financial stability and ensuring professional rugby continues in Cardiff as we approach our 150th season,” said Jones.
