Robin McBryde retired from playing in 2005 after spinal surgery
Wales forwards coach Robin McBryde will also be Scarlets' pack coach for the forthcoming season.
McBryde succeeds ex-Scarlets skipper Simon Easterby, who is expected to stay on as part of the the coaching reshuffle at Parc Y Scarlets.
The ex-Wales hooker hopes his dual role will improve his coaching.
Wales coach Warren Gatland backed the move, saying: "This new venture will undoubtedly benefit both the Welsh team and the Scarlets."
McBryde will be part of the Scarlets' set-up when Wales duties allow in a deal brokered between the Welsh Rugby Union and the Scarlets.
The Welsh regions' umbrella body, Regional Rugby Wales, have given their approval to the arrangement.
Robin brings a wealth of experience from coaching at international level, which will be good for all our players
McBryde said: "I am very grateful for this opportunity and to have more of a 'hands on' role when I'm not involved with Wales, which should benefit my own personal development as a coach, and in turn benefit the players that I coach."
Gatland added: "I know he has the skill and commitment to make it work well for us all.
"Robin will also personally benefit from the opportunity to work with a team on a day to day basis and to experience the development and progression of this side."
Scarlets head coach Nigel Davies said: "We are very pleased to have secured Robin into our coaching team next season.
"He brings a wealth of experience from coaching at international level, which will be good for all our players to be exposed to."
McBryde, who played 250 games for Llanelli and the Scarlets as hooker between 1994 and 2005, was on the Scarlets coaching staff after retiring from playing.
The 37-times capped Welshman, part of Wales' 2005 Grand Slam winning squad, helped coach the Scarlets under-18 team during the 2005-2006 season before his appointment as Wales forwards coach in 2006.
Gatland kept McBryde on in Wales' coaching team after Gareth Jenkins' departure and McBryde was part of the backroom team that guided Wales to the 2008 Grand Slam Championship.
McBryde coached the Wales team on their 2009 summer tour to North America while Gatland, Shaun Edwards and Rob Howley were part of Ian McGeechan's British and Irish Lions backroom staff on tour to world champions South Africa.
Wales defence coach Edwards also has a dual role as he is the head coach of London Wasps, but this is McBryde's first coaching position at senior club level.
The Scarlets' defence was criticised last term as the Welsh region suffered a disappointing season and failed to qualify for the Heineken Cup through the Magners League.
Davies' team only qualified for European rugby's premier competition after winning a Heineken Cup reprieve thanks the Cardiff Blues winning the Amlin Challenge Cup.