And they could not have got off to a better start in their first year of existence as they won the Celtic League.
They finished the 2003-04 season four points ahead of Ulster to win their first and, to date, only Celtic League title.
The Scarlets have reached two cup finals but twice failed to make it over the final hurdle. They lost to Munster, 27-16 in the 2004-05 final of the Celtic Cup and were defeated by Wasps in the final of the Anglo-Welsh Cup the following season.
The Welsh region also enjoyed a superb stretch of results in Europe in 2006-07, reaching the Champions Cup semi-finals before bowing out to Leicester Tigers.
The Scarlets played the majority of their home matches at Llanelli's Stradey Park before moving to a newly-built 15,000 capacity Parc y Scarlets during the 2008-09 season.
They went closest to replicating their 2003 success in 2012-13, reaching the PRO12 semi-finals.
Wayne's world
Wayne Pivac became the first Kiwi to lead the Scarlets when he took over as head coach from Simon Easterby in August 2014.
Easterby flew out to New Zealand to finalise a move which would see Pivac join as an assistant coach, but he was offered the full-time role when Easterby was appointed as Ireland forwards coach.
The Kiwi won three provincial titles during his tenure at Auckland with back-to-back successes in 2002 and 2003. His accomplishments saw him named NZRU Coach of the Year in 2003.
Pivac has also coached the Fijian national team, helping them to win the 2004 Pacific Tri-Nations and leading the Sevens side to 2005 World Cup glory.
Scarlets won 11 games out of 22 in the GUINNESS PRO12 during Pivac's first season and finished sixth - and they're still in the hunt for a top-four finish with two games to go this year.
Greatest season: 2003-04
The Scarlets could not have had a better first season, winning 16 of their 22 games in the Celtic League by four points from Irish province Ulster.
Scarlets won their first three games against Newport Gwent Dragons, away at Munster, and beat Celtic Warriors 27-22 to get their season off to the perfect start.
There were also memorable wins against Cardiff Blues at Stradey Park 35-20 and a 37-20 win over Munster, also at home.
There was a thrilling 33-33 draw with Connacht in round 17 with tries from Bryn Griffiths, Matthew Watkins and Tal Selley while Gareth Bowen was 100 per cent with his seven kicks.
Following that draw, the Scarlets won four on the bounce, including a 51-20 thrashing of Leinster, before facing Ulster at Stradey Park in the final game of the season.
Stephen Jones kicked five penalties and converted Matthew Watkins second half try to seal a 23-16 victory and ensure the Scarlets were the first Welsh side to take the Celtic League.
In the cup competitions, the Scarlets were knocked out of both the European Cup and the Celtic Cup at the quarter final stages by Biarritz Olympique and Connacht respectively.
Greatest XV
15. Liam Williams (Lee Byrne)
Just pips Lee Byrne to this 15 jersey with his 88 appearances and 23 tries for the Scarlets. After his debut season in 2011, the former scaffolder was voted Players' Player of the Season and has gone onto make 31 appearances for Wales.
14. George North
It's feels like an obvious choice to select the prolific Wales wing who has 27 tries in 59 starts for his country and scored two vital tries as part of the successful 2013 Lions squad in Australia.
13 Jonathan Davies
Another key member of the 2013 Lions squad under Warren Gatland, who also has two Six Nations titles to his name. Davies is at his second spell at Parc y Scarlets and continues to score plenty of tries.
12 Regan King
King completes his second spell at the Scarlets at the end of this season having made nearly 200 appearances and scoring 35 tries to date. A history maker when he played alongside his 18-year-old son against the Dragons in October 2015.
11 Mark Jones
Performances for the Scarlets helped launch Jones' international career in 2001 and he went on to make 47 appearances for Wales, including in the 2008 Grand Slam. After a knee injury ended his career prematurely, he joined the Scarlets coaching staff.
10 Stephen Jones
Jones kicked 18 points in the Scarlets' 23-16 win over Ulster which secured the club's only Celtic League. He made over 300 appearances for Llanelli and Scarlets over a 14-year period and has now joined the coaching ranks.
9 Dwayne Peel
Recently-retired Peel spent nine years with the Scarlets and played over 150 times and formed a strong partnership with Stephen Jones. His Wales career and three Lions caps in 2005 show just how highly regarded he was at his pomp.
1 Phil John
A Scarlet stalwart, Phil John has made over 300 appearances since joining as an apprentice in 1999. John currently holds the highest number of Guinness PRO12 appearances for the Welsh region and has scored 13 tries. He played his last home game for Scarlets against Glasgow Warriors last weekend.
2 Matthew Rees
Matthew Rees' nine years service and 57 Welsh caps means he just edges in ahead of Robin McBryde. Rees played three Lions Tests in 2009 and captained his country in nine of his 48 international starts.
3 John Davies
The contributions of the former Neath favourite and farmer Davies were vital when the Welsh region first came into existence. Samson Lee may overtake him in time, but not just yet.
4 Vernon Cooper
The former postman made 366 appearances for Llanelli and the Scarlets, many of which were as captain. He developed a great partnership with Chris Wyatt in the engine room.
5 Chris Wyatt
Unstoppable alongside Cooper, Wyatt was a natural athlete and surprisingly quick. He also made six World Cup appearances in 1999 and 2003.
6 Gavin Thomas
We've gone for Thomas here but it could easily have been Alix Popham or Dafydd Jones who were selected here. Really goes to highlight the strength of Scarlets' flankers over the years.
7 Simon Easterby
A great player and coach and was only pulled away from his beloved Scarlets by the draw of international coaching with Ireland. He played 65 times for his country and was a member of the 2005 British and Irish Lions.
8 Scott Quinnell
Last but by no means least, Scott Quinnell. Once revealed that pulling on a Llanelli jersey for the first time in 1990 was the best moment in his career. Not bad for a man with a Celtic League winners medal, three Lions caps and over 50 appearances for Wales.
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