According to multiple reports, the All Blacks and Highlanders first-five eighth has signed a two-year deal with English Premiership side Wasps.
The deal, reportedly worth an excess of NZD$1 million a season, would effectively rule the 26-year-old out of next year's Rugby World Cup in Japan.
In an emotional post on Instagram, Sopoaga said that the decision to leave was "one of the hardest decision" he's ever had to make.
"It's with a heavy heart that I announce that my family and I will be leaving NZ at the end of the 2018 season," Sopoaga wrote in a post on Instagram.
"It was one of the hardest decisions I've ever had to make but is one I'm at peace with. I have loved every minute of being a professional footballer here in NZ, I've made life long friends and memories that I'll cherish forever.
"I'd like to thank the Highlanders, All Blacks, Southland and Wellington for the awesome experiences you have provided me with over the years. Thank you to all the fans for your support it's been one heck of a ride. To my team mates and coaches over the years thank you for everything, I've been blessed to have met so many top men.
"Last but not least to my family & friends you know who you are the ones who have stood by me through the lowest of lows and the highest of highs you have seen both the valleys and the peaks, THANK YOU will never be enough!
"So here's to 2018 one last roll of the dice before I head off to experience life on the other side of the world. I'm ready."