The arrival of the 29-year-old lock will be a major boost to the Scarlets as they prepare for the new season which includes a difficult Heineken Cup draw.
The transfer of Louw from French side Clermont Auvergne looked to be in jeopardy under new regulations brought in on February 8. But the Scarlets successfully appealed to the Home Office as Louw was signed before the regulations came into force.
Scarlets Chief Executive Stuart Gallacher was pleased to have wrapped the drawn out deal up. He said: "We're delighted and looking forward to Hottie joining us in a few weeks."
The Scarlets will face Heineken Cup holders Toulouse, former champions Wasps and Scottish outfit Edinburgh following last week's draw for the pool stages of next season's competition
Llandovery are aiming to make it three titles in a row in this year's Foster's National 7s being held at BT Sport Cardiff Arms Park on Sunday 28 August. Drovers assistant coach Simon Davies and Lee Rees assess their sides chances
A pioneering strength and conditioning programme has been delivered to more than 8000 boys and girls at hub schools throughout Wales this season, helping to develop stronger, more flexible athletes for rugby and other sports.
The Singha Premiership Rugby 7s Series returns to the BT Sport Cardiff Arms Park on July 22nd when all four Welsh regions go head to head. Scarlets skills coach Dai Flanagan and Blues Elite Performance Pathway Manager Richard Hodges along with current Welsh squad members were at the launch of this season's event
GB7s women left their England base to train in Wales this week. Olympic Games hopeful Rachael Burford gives WRU TV's Graeme Gillespie her thoughts on Welsh teammate Jasmine Joyce - a 'one touch wonder'
The GB7s women's squad is currently training at Wales' Centre of Excellence where assistant coach Richie Pugh tells WRU TV's Graeme Gillespie some 'tough calls' will have to be made when it comes to finalising the 12 spots for Rio's Olympic Games.