The Scotland international was known to be leaving Glasgow Warriors and heading to Japan.
That has now been officially confirmed to the Tokyo-based side, who compete in the Japan Rugby League One.
It’s understood that Scottish Rugby offered Dempsey a lucrative two-year deal with an option for a third year but he opted to accept a four-year contract with Toshiba Brave Lupus.
The 32-year-old has been an instrumental figure in Glasgow’s success under Franco Smith, and will be difficult to replace.
It could put future Scotland selection in doubt, as Gregor Townsend overlooked George Turner when he moved to Japan due to the scheduling of their season.
However, the national team boss said previously: “Jack and I had discussions when he had the decision around staying in Glasgow or going to Japan. It was a massive decision for him.
“He was torn, because of what Glasgow have given him and the opportunities he’s had and the experience he’s had, and obviously, playing Test rugby on the back of that, but going to Japan won’t rule him out for Test matches.”
On the loss of Dempsey, Warriors assistant coach Roddy Grant said: “It is a loss. But I think the older you get or the longer you are in the game or where you see it going now, it is what it is. These things happen and people will change and that’s the reality, that’s the market, that’s, you know, so you do what you can.
“He’s been brilliant this season. The big games where he’s played incredibly well. His performance against Saracens, I think that’s probably one of the best games I’ve seen of a number eight.
“At Glasgow, we’re a very tight group and we celebrate everyone’s success. We’re pleased for him. It’s a big moment in his life in terms of career and change. And yeah, we’d really like to keep him for sure. We wish him all the best when the end of the season comes.”