The 23-year-old full-back has pedigree in both codes of rugby, having played league for Welsh-speaking school Ysgol Gyfun Cwm Rhymni, alongside Welsh international Morgan Evans.
Jones switched to the 15-man code, signing for Newport Gwent Dragons, and playing in their U-18 and U-20 academy sides.
He was also included in the Welsh RU World Sevens training squad, before returning to league in 2014, and helping Aber Valley Wolves to finish top of the South Wales Conference.
“I’m really looking forward to the challenge,” Jones said.
“I know that League 1 will be a big step up from the Welsh Conference but I hope I can bring something to the team and we can have a successful season.”
Scorpions assistant coach Paul Emanuelli believes that the player’s pace will help to make him a real handful for opponents this season.
“Sion has been fantastic since he started training with the club a few weeks back,” he said.
“He is one of a few people we’ve had in on trial and has really impressed.
“He’s sharp, strong and has picked up our game structure extremely quick. We’re looking forward to him getting a chance and seeing how he goes.”