The All Blacks wing has endured a frustrating Super Rugby campaign with the Highlanders this year and hasn't played since suffering a knee injury at training last month.
However, he could return to action during the team's upcoming trip to South Africa.
While the length of the contract was not revealed, Naholo was glad to have secured his future with London Irish. But the 28-year-old said he was still 100 per cent focused on his short-term goals with the Highlanders and All Blacks.
"I'm looking forward to the opportunity of playing in the UK but I'm still very much focused on the present and want to work really hard with the Highlanders to ensure we finish our season on a high," Naholo said.
"I feel like I owe it to the Highlanders after all that has happened to me since I came down here in 2015 - it really changed my life. I'm very appreciative of everything the club has done for me and our fans are the best in the world. I also have other goals I'd like to achieve with the All Blacks in 2019, and I know our Highlanders fans will be right behind me all the way."
Naholo first played provincial rugby for Wanganui as an 18 year old schoolboy.
The Fijian-born flyer has played 58 games for the Highlanders, after shifting from the Blues in 2015, and his dazzling form that year earned him a Super Rugby title and All Blacks' selection.
He debuted for the All Blacks against Argentina in Christchurch in 2015 and famously recovered from a broken bone in his leg to play in the 2015 World Cup.
Naholo has scored 16 tries in 26 tests for the All Blacks, but is under pressure to make this year's showpiece in Japan having struggled for form before his knee injury struck.
But All Blacks coach Steve Hansen said he was still very much in contention.