Pritchard will join the Bulldogs in 2011 after eight seasons with the Panthers, where the New Zealand international carved out a reputation as one of the most destructive forwards in the game.
He will form a dynamic backrow combination at the Bulldogs alongside Andrew Ryan and David Stagg, with Pritchard's acquisition set to see Jamal Idris return to the centres.
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"Frank has got size, he's got speed, he's got strength and is a player that has a great impact on games," Bulldogs coach Kevin Moore said.
"We're thrilled that we'll be able to welcome him to the Bulldogs next year.
"In the past couple of seasons we've lost several of our senior players and I'm expecting Frank will step up to take a leadership role within our team."
Pritchard, 26, has played 141 first grade games since making his debut for Penrith in 2003 and has played 18 Tests for the Kiwis.
