With 59 appearances to his name, Somerville is currently the most-capped prop in New Zealand history. The 30- year-old, who was part of the All Black side which earned a Second Test victory over England in Christchurch last Saturday, can play on either side of the scrum.
"The market is now making players of Greg's experience, calibre and undoubted expertise available and, once we appreciated his interest and desire to add significantly to our squad, we were thrilled to sign him," Gloucester boss Dean Ryan told www.gloucesterrugby.co.uk
"To have represented the All Blacks in more than 50 Test matches and be versatile to operate on either side of the scrum, means he is an outstanding acquisition for us at this stage of his career.
"With the likes of Christian Califano and Patrice Collazo leaving the club, we needed an option that could benefit us long-term and we have managed to combine experience, versatility and expertise in one package and that is fantastic for the club."
Somerville made his debut for Canterbury in an NPC semi-final in 1998, was a Crusader the following season, and an All Black within two years of his first representative appearance.
He made his Test debut in 2000 against Tonga and the Hawke's Bay-raised prop became the fourth man to play a century of matches for the Crusaders when he featured in the 2006 Super 14 semi-final victory over the Bulls.
Somerville said: "I have achieved virtually everything possible in New Zealand rugby and to have represented the All Blacks will always be something very special to me.
"But this opportunity has developed and the chance to experience a new culture for myself and my family, and contribute to a side that is already right at the top of the English Premiership was an exciting opportunity to take up.
"I am looking forward to contributing to Dean Ryan's side and proving myself in different conditions and against different opponents. Gloucester's front row options are already very talented and I am looking forward to adding to that mix next season."