Dragons coach Paul Turner said: "It was important that we secured the signing of a world class forward and Colin fits that description.
"He is a big, strong forward and is a huge boost for the region. He is a proven leader and has a vast amount of experience.
"It's a huge statement of intent and ambition. I've been talking to Colin over the last two months and I was impressed with his ambition both at regional and international level."
Charvis, who has won 84 Test caps, had seemed set to retire when he was released by the Falcons.