24-year-old Sopoaga has played 49 games for the Super Rugby champions and made his All Blacks test debut this year against the Springboks in South Africa.
He currently holds the season record for points scored by a Highlander with 191 in 2015 and is the second-ranked Highlander for most career points on 453 (behind current assistant coach Tony Brown).
Sopoaga's accurate boot and skilful running game are credited with helping the southern men to their first ever Super Rugby title this year.
"I'm so grateful for the opportunity to sign to the Highlanders until 2018. I owe a lot to the coaching staff and the organisation for sticking by me and allowing me to develop not only as a player but as a person. I wouldn't be where I am today without the great team culture, teammates, coaches and medical staff. I'm looking forward to my future with the club," Sopoaga said.
Sopoaga joins teammate Aaron Smith, who also announced a lengthy contract extension earlier this year, their commitment to the team augurs well for the future prospects of Highlanders' rugby.
Both Sopoaga and Smith have been nominated for the Investec Super Rugby Player of the Year at the Steinlager New Zealand Rugby Awards being held in December.
Sopoaga and Highlanders teammate, Waisake Naholo, are currently in England with the Barbarians preparing to take on Argentina on the 21st November.
