Van der Merwe attended Grey College in Bloemfontein before joining the Bloemfontein-based provincial side the Free State Cheetahs.
He immediately established himself as a first-choice player for them, making eleven starts and two substitute appearances in the 2009 Currie Cup Premier Division.
He also featured in 39 first class matches for the Blue Bulls between 2009 and 2012, with national team call-ups and injury preventing him from playing for them in 2013 and 2014.
Shortly before the 2015 Super Rugby season, the Bulls announced that Van der Merwe would leave after the 2015 Currie Cup Premier Division to take up a contract with French Top 14 side Clermont.
He missed out on selection to the 2011 Rugby World Cup, but established himself as a regular for the team over the next few years, appearing in 36 test matches prior to his move to Clermont in 2015.