The hulking 25-year-old, who plays Super Rugby for the Auckland Blues, won his 15th cap for the All Blacks against Italy in November and his departure comes as a surprise for New Zealand Rugby two years out from the World Cup in Japan.
Bristol, currently bottom of the Premiership with two wins from 14 games, made no mention of the length of his contract but Luatua said in a club statement that he was looking forward to contributing to the club's "long term vision".
"I have a fantastic relationship with Pat (Lam) and I enjoyed working with him at the Blues," he said on Bristol's website (bristolrugby.co.uk).
"I've heard great things about the environment that is being built there and the plans in place, so I can't wait to get started in the summer."
Luatua has played most of his test rugby as a blindside flanker but is a capable number eight and can also play in the second row.
He made his All Blacks debut off the bench against France as a highly-rated 22-year-old in 2013 but struggled to nail down a regular spot, with veteran Jerome Kaino owning the blindside spot in Steve Hansen's back row over the past three years.
With Kaino set to turn 34 in April, however, Luatua may have been afforded more chances to impress Hansen before the 2019 World Cup.
Although aware of Luatua's move, the announcement from Bristol blindsided the Blues, who declined to comment.
All Blacks captain and number eight Kieran Read told local radio he was "really disappointed" by Luatua's departure.
