Sowden-Taylor will bolster the Dragons' back-row options and compete with fellow international Gavin Thomas for the number seven shirt.
The 28-year-old said: "I'm really glad to have signed with the Dragons, it has taken a fair bit of time but I felt I needed that and now I'm just happy to be here.
"The main reason for my move was to get regular rugby. That is something I have struggled with a bit with Cardiff and I don't think I have been able to reach my full potential. With a World Cup coming up I really think I can push for an opportunity. I feel that if I am on top of my game I am more than capable.
"Obviously Gavin Thomas is here and he is a quality player. But the way rugby is played these days it is important that the regions have strong squads. There are a lot of hard games and if you look at most sides they have quality players in every position.
"I thought the Dragons had a really good season last year and I'm looking forward to being part of the side. There is a good group of players here and hopefully we can push for silverware."
Factfile - Robin Sowden-Taylor
DOB 9th Jun 1982
Height 1.85 m (6' 1")
Weight 100 kg (15 st 10 lb)
Position Back Row
Honours Wales (8 caps)