He represented the Stormers in Super Rugby, having made his debut during the 2008 season. He also played for Western Province in the Currie Cup. Louw was part of the Stormers team that lost the 2010 Super 14 Final to the Bulls. Following the Super 14 season, Louw made his debut for South Africa against Wales at the Millennium Stadium in Cardiff. He played the entire game as South Africa won 34–31. Louw was selected for South Africa's next match in the mid-year tests, against France at his home ground, Newlands Stadium in Cape Town. Louw scored the last of five tries, helping South Africa to a 42–17 victory. After taking part in South Africa's victorious two match series against Italy, including a try in the first Test, Louw made his Tri Nations debut in July 2010. It was the first time Louw experienced defeat as a Springbok, with New Zealand winning the game 32–12. Louw has been one of the best flankers in the Western Cape in 2010 and 2011, winning man of the match awards at Test level, and helping the Stormers become the stingiest defensive squad in the Super 15. On 19 March 2011, he played admirably against the formidable Deon Stegmann and Dewald Potgieter, in a brutal North-South derby, stealing the ball at breakdown.
He is a Springbok candidate for the No. 6 jersey (No. 7 elsewhere) in the World Cup, because he is big enough to create havoc at the breakdown and be a lineout option.
On 12 July 2011 it was announced that Louw signed for Bath Rugby on a 3-year deal.