“Loftus and the Bulls have always had a special place in my heart and I look forward to coming back home,” tight-head van der Merwe said.
He made 98 appearances for Toulon in four seasons and started 2017’s Top 14 final loss to Clermont.
Super Rugby has been suspended since mid-March but holding the domestic Currie Cup, set to start later in the year, remains on the cards.
On Friday, the Pretoria-based franchise announced head coach Pote Human had left his position five months early.
“It is important for Jake to get the backing and support from all stakeholders. He certainly has my support and I wish him all of the best,” Human said.