The 28-year-old Rugby World Cup winner, who has 26 caps, has also won a Super Rugby title and was part of the successful Baby Black World Rugby U20 Championship team.
He has regularly shown his finishing capability at all levels, crossing the whitewash 16 times at international level alone, with a further 41 coming in his 55 Super Rugby appearances for the Highlanders, a franchise record.
London Irish director of rugby Declan Kidney is looking forward to seeing Naholo in action for the Exiles later in the year once his New Zealand contractual commitments have been completed.
“Waisake is a top-class player who will bring great experience with him, which we hope he can pass onto our younger players as they continue their development with us,” he said.
“We are delighted that a player of his ability and age profile has bought into our vision for where we as a club are working hard to get to. We look forward to welcoming him to Hazelwood when he is finished with his commitments with the NZRU.”