"I'm really looking forward to the switch. It's exciting to be joining a squad with the amount of young talent that the Dragons has at the moment. I'm eager to press for some more game time and hopefully help push for a successful season here at the Dragon," said Evans.
The 23-year-old Evans rose through the ranks at the Scarlets and became a mainstay of the side over the past three seasons. He made 14 appearances for the Scarlets last season and won two caps on Wales's 2009 North America tour.
Prydie holds the distinction of being the youngest player to represent Wales and to score a try for this country. He has four Welsh caps, has played on the IRB Sevens circuit and made seven appearances in the Aviva Premiership for Wasps during his loan move.
Recently named in Danny Wilson's Wales Under 20 squad for the IRB Junior World Championships in South Africa this summer, Prydie will link up with new team mates Jon Evans, Jack Dixon and Ieuan Jones in the tournament.
He made his Ospreys debut at the age of 17 years and 292 days when he came on as a second-half replacement in the Heineken Cup match against Viadana in December 2009 - an appearance that made him the youngest player in Heineken Cup history.
"I'm really looking forward to the new challenge that signing with the Dragons presents. I've worked with Darren Edwards before and felt I learned a lot from the time I spent with him," said Prydie.
"This season has felt a bit stop start, so it will be great to have a fresh start and a bit of consistency. There is a lot of potential at the Dragons and hopefully we can be very competitive next season."