Scott, 23, is one of a number of key Scarlets players in their international ascendancy who have come through the Scarlets development system with Williams starting out his regional rugby career as part of the Scarlets Academy aged 18 after playing community rugby at his home club of Newcastle Emlyn.
Speaking about his new contract with the Scarlets Scott Williams said: "I'm really pleased to have secured my contract with the Scarlets going forward and to have committed my future to rugby in Wales.
"It's really good to have this all secured now, so I can concentrate solely on my rugby and the campaign ahead of us, both with Wales in the Six Nations and then back to RaboDirect PRO12 league action with the Scarlets."
Scott Williams joined the Scarlets in 2009. Born in Carmarthen, Williams grew up in Newcastle Emlyn and went on to play for Whitland RFC and Llanelli RFC.
He made his Scarlets league debut on 2 October 2010 against the Ospreys at Parc y Scarlets and later made his international debut for Wales as a replacement against the Barbarians on 4 June 2011.
He was selected for the Welsh squad that went to the 2011 Rugby World Cup in New Zealand and scored 4 tries, including a hat trick against Namibia. Williams was also part of the Grand Slam winning squad of the 2012 Six Nations Championships and scored the decisive try in the victory over England at Twickenham.
Williams has scored four tries this season, three of them in the Heineken Cup - two against Harlequins and one against Racing Metro. He has 24 caps for Wales, having played for Wales U20 in 2009 and 2010 and represented his country at both U16 and U18.
Scarlets Head Coach Simon Easterby expressed his delight that Williams will remain at the Region that has been his rugby home since his rise from age-grade to prominence on the international stage.
He said: "Scott is an exceptional talent, he has shown his maturity and skill now on the big stage. He is everything you need from a top-class centre - he's powerful, quick and decisive with a very good passing and kicking game. We are all delighted that he's staying at the Scarlets and committing his future to our Region. It's great news for our whole rugby community from the coaches, to our Scarlets players, supporters, sponsors, partners and all those involved in supporting and developing talent in our region.
"Given all the debate about retaining our best players in Wales, it's a real positive for Welsh rugby as a whole that one of our top internationals has chosen to stay here to play his rugby.
"Scott is an excellent professional; he works hard, is ambitious, competitive and works well within the Scarlets team dynamic - setting high standards for himself and others. He thoroughly deserves the positive recognition and profile he has received as a player both for the Scarlets and Wales and there was a lot of demand and competition to secure him in contract.
"It's very significant and important to our Region to have extended Scott's contract as a key player to build our squad around. We're proud that someone of his ability, experience and with a genuine passion for our region, has committed to remain with us in the seasons to come."
Scott Williams commits to @Scarlets_Rugby! A world-class signing! #RaboPRO12 http://t.co/vVSlN1hRe6
- RaboDirect PRO12 (@RaboDirectPRO12) February 6, 2014
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