"This is a really hard decision to have made as I've loved every minute of playing at Kingsholm," Somerville explained.
"I just feel that now is the right time for my family to be nearer home, particularly with our third child being born just before Christmas."
"The experience of playing in the Premiership has been awesome, and I'd like to thank everybody at Gloucester Rugby for making our time here so enjoyable."
"The backing from the Gloucester supporters throughout has been exceptional, and in particular it's been humbling to receive so many good wishes during my recent injury. Kingsholm is a very special place to play rugby and it's been a privilege to play in front of such a loyal crowd."
Head coach Bryan Redpath added:
"Greg's contribution on and off the field has been exceptional as you would expect from somebody capped so many times for the All Blacks."
"The knowledge he's been able to pass on to the younger props coming through has been invaluable and Paul Doran-Jones, Rupert Harden and Shaun Knight are all better players having had the chance to work and train alongside Greg."
"Though we will miss him, Greg has been a great servant to Gloucester Rugby in his 18 months with the club and he and his family will depart at the end of the season with our best wishes."