The former Waikato captain played 77 times for the 2011 ITM Cup finalists before moving to Leinster on a one-year deal last season.
To date he has 14 caps for Leinster, including five in the Heineken Cup, and will be brought into the Connacht team to strengthen the depth of the squad in the crucial tighthead position
The dynamic front row forward is known for his ferocious scrummaging and exceptional leadership skills and during his time as the Waikato skipper, he led names such as All Blacks legends Marty Holah, Stephen Donald, Mils Muliaina and Sitiveni Sivivatu
"Nathan's a proven leader both on and off the pitch and I am looking forward to working with him here at Connacht."
Connacht's team manager and White's Kiwi compatriot, Tim Allnutt, added: "To have someone of Nathan's calibre and work ethic joining the squad is a huge boost to the province.
"Ronan Loughney has been doing a superb job at tighthead this season and Nathan's signature will add an extra layer of depth to this vital position.
"With a three-year deal Nathan has shown he believes in what we are doing here and we will use his knowledge and experience to help bring the next crop of props through our Academy structures."