27 year old Thomson, has been part of the Hurricanes club since 2013, making 40 appearances. That number would have been significantly higher had he not suffered two serious shoulder injuries in recent seasons.
Equally adept at No 8 or lock, the former New Zealand Under-20 world champion and Maori All Black said he was determined to help the Hurricanes fulfil their potential and win another Investec Super Rugby title before he headed to the Welsh club.
"My focus is fully on finishing the current season on a high with the Hurricanes and hopefully lifting some silverware.
"The Hurricanes have been a massive part of my rugby career and I want to do all I can to make this year as memorable as possible."
Hurricanes head coach Chris Boyd has no doubts Thomson will continue to play an integral part in the 2018 campaign.
"Blade has become a senior member of the Hurricanes and has always been a really important part of our squad," he said.
"He has played a significant role for us and I'm sure that will continue. We obviously will wish him well when the time comes but as Blade has pointed out, his focus remains on doing what he can to make this season as memorable as possible."
The Scarlets were on the look out for a player following confirmation that Tadhg Beirne and Scotland skipper John Barclay were leaving at the end of this season.