The 2010–11 Celtic League season saw van der Merwe come into his own, starting 19 matches and picking up 9 tries along the way. Van der Merwe finished as Glasgow's highest try scorer for the season as well as finishing tied for third with Jonathan Davies in the Celtic League's leading try-scorer category. Van der Merwe also started 5 matches and score 3 more tries in the 2010–11 Heineken Cup.