Van der Merwe was signed by Pro14 side Cardiff Blues for the 2017 season, however on 1 August 2017 he was released by the club due to club based "financial challenges".[citation needed]
On 25 August 2017, he was named amongst the starting XV for a pre-season friendly game for London Irish against Richmond on a club trial.[4] On 31 August it was announced he had been signed by the club.[5] He was released ahead of the 2020–21 season.[6]