The 6ft 7in threequarter, younger brother of the former Bradford and St Helens stand-off Leon Pryce, was a free agent after being released by the Bulls at the end of last season.
"Naturally we are delighted to have been able to bring in a player of Karl's undoubted quality," said Dewsbury coach Glenn Morrison. "He's played at the top level for a lot of years and will bring so much to the club."
