The 27-year-old lock has been with Harlequins for the last two years and has impressed with his athleticism and skill at set-piece. Prior to his time with the English club he played with Parma in Italy.
Born in Rosario, Vallejos has represented Argentina in the U17, U18, U20 and U23 age groups as well as achieving his first cap for the Pumas after featuring for his country in the 2011 Rugby World Cup.
The Scarlets confirmation of Vallejos joining their squad next season adds to the signing of another key second row talent, South African George Earle. Earle, 25, who was born in Durban, has been a prominent player with the Super 15 team this year making nine appearances. The 6 ft 6" and 17st 5 lock has impressed in the Super 15 competition this year and is highly regarded as a first-class line-out jumper and dynamic in open play.
Scarlets Head Coach Simon Easterby said: "We're delighted to announce formally that Tomás will be joining our squad for next season.
"He is a player we have followed closely throughout last season while he was at Harlequins and believe he can bring a new dimension to our second row options enhancing and strengthening our set piece play. We want to bring in players that are the right fit for us as well as complementing the players we have here already.
"He is an excellent line-out forward, an athletic player and exactly the type of player we see fitting well with the way we want to play at the Scarlets going forward and our ambitions for the future.
"We have been clear that we would be committed to strengthening our second row options as part of our further progression next season and its positive for the region and the wider squad will have two talented, ambitious international-class players joining us next season. It adds to the dynamic in the squad with two players that we believe can really add an edge to our game.
"We've been working with Tomás for several weeks regarding the final arrangements for his move to Parc y Scarlets after securing him last month, and it's great to see the enthusiasm he has for the Scarlets as a rugby region. He's excited and motivated about the move here with the players he'll be joining and our style and ambitions for next season both in the RaboDirect Pro12 and European competitions."
Biography
Tomás Vallejos
DoB: October 16th 1984. Age 27.
Born: Rosario, Argentina
Height: 6 ft 5"
Weight: 113kg
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland