The 26-year-old will join Cardiff on an immediate short-term deal, to offset the injury loss of inside backs like Rhys Patchell.
Tuifua's arrival will also prove timely with the RBS 6 Nations all set for kick-off in less than two weeks.
Cardiff's new addition is expected to arrive at the Arms Park later this week.
"Isaia is a very strong ball carrier and defender who will add to our squad," said rugby director Phil Davies.
"We have brought him in initially until the end of the season to look at him and provide us with cover with the injuries we have to the backline.
"We feel Isaia's style of play will complement the likes of Dafydd Hewitt, Gavin Evans and Richard Smith and give us another option.
"It gives us depth in midfield as other players come back from injury."
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