The contract extension sees him join a strong pool of international players already signed up for the 2016-17 season at Parc y Scarlets. Captain Ken Owens leads an impressive group of players who have committed their futures to Scarlets Rugby including Jake Ball, Rob Evans, Rhodri Jones, Samson Lee and Liam Williams.
On the other end of the spectrum, and also committed for the foreseeable future, are some of the brightest young local talents including centre Steffan Hughes, fullback Steffan Evans, hooker Ryan Elias and outside half Daniel Jones showing Scarlets' continued commitment to developing the next generation of Scarlets.
29-year-old Barclay has proved to be an invaluable asset for the Scarlets since joining the region in the summer of 2013 and was dismissed from Scotland Rugby's final 31-man squad for the 2015 Rugby World Cup.
He was included in the PRO12's top turnover winners in 2014-15 and his versatility has seen him play blindside flanker, openside flanker and number eight. The experienced loose forward has also taken the role of captain in Scott Williams and Ken Owens' absence including the opening home victory over Ulster earlier this month.
Commenting on the news Scarlets Head Coach Wayne Pivac said: "It is fantastic to see John committing his future to the region given the experience that he brings to the environment.
"John gives us a great service across the back row as he plays equally as well at 7, 6 or 8. Despite playing half the season in the number 8 position he was still named in the top three players for turnovers in the PRO12 last season. He's a leader on the field and a leader in our group."
John Barclay added: "I'm delighted to have extended my contract with the Scarlets. It's a great place to play and live and we've really settled in as a family.
"The investment in the environment in recent times is proof that the region has ambitions to succeed at the highest level and it's a great place for myself to continue developing as a player. We are fortunate to have a group of talented young players here; the truth is I'm learning a lot off the new guys and it's really fun to play with them."
Scarlets General Manager of Rugby Jon Daniels said: "Recruitment for 2016-17 and beyond has been underway for some time now. In addition to those already committed, our priority has been to re-sign a group of key players and John certainly falls into that category."
Barclay and his fellow Scarlets will be back in action at the Parc on Friday 16th October when they take on Leinster in the Guinness PRO12, kick-off 7.35pm. Tickets are on sale now at tickets.scarlets.co.uk or by calling 0871 871 8088.
