The former Wales Under 20s captain, who led the side to a first-ever victory over New Zealand in the Junior World Championships in 2012, penned his first senior contract in 2011 having worked his way through the Region's Academy beforehand.
With an injury to Owens Myhill had an opportunity to stake a claim for the hooker's jersey early on this season, alongside Emyr Phillips, before himself tearing his pec in the Welsh derby victory over Ospreys at Parc y Scarlets in the first game of 2015.
Since making his senior debut for Scarlets, in a league match against Leinster in March 2011, Myhill has gone on to make 54 regional appearances scoring three tries including three European Rugby Champions Cup appearances against Toulon, Leicester Tigers and Ulster this season.
Commenting on the news Head Coach Wayne Pivac said; "Keeping local Welsh talent at the Region is a very important part of our development and we are delighted to see Kirby join an already strong band of front rowers committing their futures to the Scarlets.
"After a strong start to the season he suffered a setback with an injury against the Ospreys at the start of the year but he will be an important player for us as we return for the new season in a World Cup year."
Pembrey's Kirby Myhill, who played his early rugby with Burry Port and Kidwelly RFC said; "I'm delighted to have signed a new contract with the Scarlets. It's been a frustrating few months for me personally but I'm coming to the end of my recovery and am looking forward to making a return to action.
"Growing up just down the road from Stradey Park, and heading to the ground to watch games as often as possible, representing the Scarlets was always something I wanted to do. I'm very much looking forward to further developing my game with the Scarlets next season."
Scarlets player announcements for 2015-16 thus far;
Extended - Liam Williams, Ken Owens, Rob Evans, George Earle, Lewis Rawlins, Phil John.
NDCs: Rhodri Jones, Samson Lee, Jake Ball, Scott Williams.
New: Glasgow and Canadian winger DTH van der Merwe, outside half Aled Thomas from Gloucester, tighthead prop Will Taylor from Wasps, lock Tom Price from Leicester Tigers, Welsh qualifies loosehead prop Dylan Evans, number 8 Jack Condy from Cross Keys.