Pryce, 29, is one of the most decorated players in the modern era, winning four Super League titles, five Challenge Cups and four World Club Challenge medals in his spells at first Bradford and then Saints.
Catalan head coach Trent Robinson said: “One of our targets for 2012 was to target an England international player who has the ability to change a match. Leon definitely fits these criteria and we are looking forward to his contribution to the progression of rugby league at the Dragons.
“He will be the first British Lion to play for the club and should be commended on his courage to make the step across the Channel. He has a proud history at both Bradford and St Helens and he is clearly focused on 2011 and his commitment to the great club.”
Pryce said: “I have had a great time at Saints and have nothing but brilliant memories of the club and the team. I have been a part of several trophy winning sides and it has been an honour to play with so many great players and teams over the years.
“I would also like to thank the fans for their support; they have been nothing but top class in my time at the Saints. They were patient with me when I was out injured and their support when I came back will be something I always remember.”
Catalan Chairman Bernard Guasch added: “After that of Stacey Jones, the signing of Leon Pryce is one of the high points of our history. This is one of our biggest recruits in six years and is a great honour for the club. The signing is recognition that six years of hard work have gained us the trust of major players like Leon Pryce.
“It is also our first signing of an English player since we joined the Super League and we are proud that it is of a player of the calibre of Leon Pryce. His arrival, like that of Louis Anderson, should allow us to have greater ambitions, to aim even higher, next season.”