Unlike fellow recent union converts Andy Farrell (Saracens) and Chev Walker (Bath) though, 20-year-old Pryce's move features no Rugby Football Union funding and will be solely financed by his club.
The 6ft 6in Pryce was a prolific try-scorer for the Bulls, and he becomes Gloucester's second major league import after Henry Paul, who has now returned to the 13-a-side code with Harlequins.
Ryan said: "Karl's try-scoring record for Bradford speaks for itself. He has enormous pedigree and will prove a significant addition to the Gloucester squad.
"We have been watching him for some time and believe that his physical presence will complement our other options in the back line.
"Rather than bring someone over from rugby league who only has a couple of years remaining at the highest level, in Karl we have a young player who we can work with to develop his skills and make a force in rugby union."
Pryce will hope to make an early impact for a Gloucester side currently unbeaten in the Guinness Premiership.
"I am delighted to be joining Gloucester, and I cannot wait to hit the ground running," Pryce said.
"I had a wonderful time at Bradford, and I want to thank everyone involved with the club, including an amazing set of supporters, for some fantastic memories.
"We've had another good season, but when the opportunity arose to try a different code and challenge myself in new arenas, it proved too strong to resist.
"I took advice from a number of people closest to me, and without exception they said Gloucester was the right club to be at.
"They have a fantastic set-up, excellent training facilities and quality coaches who I know I will learn from."