The 28-year-old will link up with the Scarlets next season, having made almost 150 Premiership and Heineken Cup appearances in Gloucester colours.
Scarlets rugby director Phil Davies said: "We have a lot of young players coming through at Stradey Park, and Adam offers a bit of experience.
"I am sure Adam will do a good job for us, as he has gained plenty of experience playing both in England and Europe."
