The strong and powerful 27-year-old Nigerian winger, previously with London Welsh and Richmond, played 25 games for Llandovery last season and scored 11 tries. He also broke into the Scarlets team last season with three appearances, his first start in the jersey playing against Ulster in the Magners League.
He said: "I'm really pleased to be signed up with the Scarlets now full-time and just look forward to the challenge ahead and working hard in pre-season to get myself in great shape. I know I need to work on the finer points of my game and I'm looking forward to being part of the Scarlets squad next season.
"Although I had some time with them last season, I'm new to the Scarlets mix and have plenty to learn from the guys around me - from simple things like the game language and team culture to the technical dynamics within the Scarlets environment. It's a great set-up, a really good bunch of guys and there's a good atmosphere within the squad. I'm really looking forward to be part of that next season and I'm eager to impress so will be do all I can to learn quickly.
"I've been enjoying my time in this part of the world, the Scarlets have great supporters who are really passionate about their rugby and I've been made to feel really welcome."
Head Coach Nigel Davies said: "Joe has speed and power and is a player with a lot to offer - he's one of those players with a certain X-factor and you need players like that in the mix in a team. He will benefit from being with us full-time and as part of his development contract will get mentoring not only from the coaches but also the senior players who will be helping him work on key areas of his game."
Joe Ajuwa was born in Lagos, Nigeria and moved to the UK with his family (which includes nine brothers and three sisters!) in 1994. He first played rugby at school in Bath then played for English students while he was at University. His childhood rugby hero was Jonah Lomu. Brothers Daniel and Shadrack Ajuwa have played for Bristol RFC.
And the Scarlets have also signed full-time senior playing contracts with two promising young West Wales talents - flanker Aaron Shingler and hooker Emyr Phillips who were both on development contracts with the region last season.
Llandovery product Emyr Phillips, 23, played 10 competitive fixtures as part of the Scarlets squad this season as well as 13 games for Llandovery RFC.
Shingler, (6' 6") aged 22 grew up in West Wales, attending Pontarddulais Comprehensive School and Gorseinon College. A competitive, former all-round cricketer he signed to the senior Glamorgan team for 2007 season before concentrating on rugby. He played 23 games for Llanelli RFC last season, scoring 5 tries and two games for his region against Connault and Harlequins. His brother Steven Shingler, who plays for Wales Under-20s has also played with Aaron at Llanelli RFC.
Scarlets wing and Wales sevens player Darren Daniel, whose contract with the Scarlets came to an end this summer, will leave the region to join Carmarthen Quins next season. Daniel, who is from Burry Port has been with the Scarlets for five seasons, making 65 appearances and scoring 21 tries in total. He made two starts for the Scarlets last season, playing most of his rugby for the Quins during the 2009/2010 campaign.