Morgan, who made his first start for England against Wales after coming off the bench against Scotland and Italy, still had a year left on his current contract at the Scarlets to run.
However Gloucester have agreed a deal to take the 23-year-old to Kingsholm in the summer
Morgan, who was born in Bristol, said: "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."
Gloucester head coach Bryan Redpath is thrilled to have secured the signing of Morgan, particularly as both Luke Narraway and Alasdair Strokosch are off to Perpignan in the summer.
"Ben joining us is a very significant signing," said Redpath.
"He's a big ball carrier who also possesses great handling skills.
"He'll help get us over the gain line and also do his bit in defence.
"He's international quality and still only 23 years old. He still has so much upside and I think he'll be a great addition to our squad."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
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The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.