Bok prop signs for Toulon
Van der Merwe has been with the Bulls since 2014 - he previously played for the Cheetahs as well.
He also has racked up seven Test caps for Springboks during Heyneke Meyer's tenure, but was not included in Allister Coetzee's 31-man squad for the upcoming three-Test series against Ireland.
Meanwhile, Jamba Ulengo and Pierre Schoeman have both extended their contracts with Bulls until October 2018, the Blue Bulls Company (Pty) Ltd confirmed on Thursday.
Ulengo, a former Springbok Sevens player, has moved from Stellenbosch to Pretoria last year and after a high-scoring season for the Blue Bulls in the Currie Cup last year, continued with that for the Bulls in 2016.
He has scored four tries in seven appearances on the wing for the Bulls.
Schoeman, a former Junior Springbok representative, is a local player who has represented the Blue Bulls from junior level. He made his Super Rugby debut in 2016.
Xander Janse van Rensburg, High Performance Manager of the Blue Bulls Company, expressed his delight with the extensions.
"There is no doubt that both Jamba and Pierre will be pushing for national honours sooner rather than later and to have two of the most talented players around at Loftus Versfeld for the next two years is great news," said Van Rensburg.
"It is not only good news to our effort to build something special here at Loftus, but also to our fans, who will be able to enjoy the talents of these players for another two years."