Nadolo was the third highest try-scorer in Super Rugby last season with nine in 13 matches and will be a big loss to the seven-times champions when he departs to take up a three-year deal in France.
Crusaders coach Todd Blackadder said Nadolo had exceeded expectations on and off the field since moving to New Zealand in 2013.
"Nemani is one of those special players who only come along every once in a while," he said in a news release. "He is built like a tank but has skills and speed that defy his size.
"We will certainly miss his presence but we are grateful for the time we’ve had and can’t wait to unleash Nemsy on the competition again in 2016."
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The 27-year-old grew up in Australia and after failing to establish himself at the New South Wales Waratahs revived his career in Christchurch after spells in England, Japan and in France with Bourgoin.
"I honestly never thought, before getting offered a position with the Crusaders, that I would get to play Super Rugby again," Nadolo said.
"So making the decision to leave a team that has given me that opportunity and shown such faith in me was definitely not an easy one to make.
"But I still have a season to go here first and I intend to make my last season here a great one and leave on a high note."
Nadolo's hopes of making a major impact on the international stage at this year's Rugby World Cup were hampered by injury although he did score tries against England and Uruguay and kicked eight points against Australia.
(Reporting by Nick Mulvenney in Sydney, editing by Peter Rutherford)
