The 36-year-old All Blacks great, who played two seasons for the Blues in 2012 and 2014, is returning to the franchise on a one-year deal next season.
A source close to Nonu confirmed the deal to 1 NEWS before a formal statement was released by the franchise later in the afternoon (New Zealand time).
"Hopefully next year will be a year to build and to be successful. That is the challenge I am looking forward to," Nonu said in the statement.
"I know the Blues have had some tough times in the last few seasons but I am excited to play with some of the young and up-and-coming players who will have long careers and rejuvenate this place.
"And I am looking forward to be under the watchful eye of Tana who was a mentor when I was coming through, so I am looking forward to doing my best for him and the franchise."
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