He could have qualified for Wales under residency rules but opted to play for England, the country of his berth, and has enjoyed a fine first RBS Six Nations.
The powerful number eight has joined on a three year contract. "It's a great opportunity for me and one that I'm looking forward to immensely. I grew up just down the road so Gloucester is my local team and I can't wait to run out at Kingsholm for the first time.
"Gloucester have some incredible talent in their squad and play a great style of rugby. Bryan Redpath's told me of his plans for next season and beyond and being part of it is an exciting prospect."
Morgan was quick to pay tribute, however, to the Scarlets for helping him to get to this point in his career.
"I wouldn't be where I am today if it weren't for the Scarlets and I'm incredibly grateful to so many people for the help they've given me along the way.
"Having opted to pursue an international career with England, they understood my desire to play in England and have been brilliant in the way they've handled things."