Sandow said: “I was really impressed with the direction the Eels are heading under Steve Kearney. He is clear on where he wants to take the team and I’m excited to be a part of that future.
“It was a very hard decision for my family and me but I’m really looking forward to joining the Eels next year.
“But for now my focus remains with Souths and I am 100 per cent committed to the rest of the season with my teammates.”
Eels coach Steve Kearney said: “Chris is a young halfback with a lot of potential and he’ll be a great asset with regards to what we’re building here at the club.
“This is the first step in our recruitment drive and we’re looking forward to building on the solid talent base we already have.”