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
WRU International Skills Coach Jason Strange is a busy man, combining the new role with that of Wales Under 20 attack coach, Ebbw Vale head coach and continuing to teach at Ebbw Fawr Learning Community.
Warren Gatland and Sam Warburton look ahead to this week's crunch RBS 6 Nations tie against France, where the Wales skipper in particular is keen to make his mark, as Paris has proved a bleak place for him in the past.
Following their historic win over England, Wales Under 20 suffered a narrow, 36-34 loss to their Scottish counterparts last weekend, despite outscoring them by five tries to three. Watch the match highlights and reaction.
WRU TV go behind the scenes with the Wales squad as they put the final touches in place ahead of the clash against Scotland at Murrayfield. Follow the squad on their captain's run, the kickers visit to Murrayfield and Neil Jenkins' press conference