The Canadian has spent the majority of his professional career playing in the United Kingdom after initially signing for Saracens in 2007.
Van der Merwe went on to sign for Glasgow Warriors in 2009 and he made 96 appearances before heading to Wales with Scarlets.
The winger was drafted in by Newcastle in 2017 but he failed to make much of an impact and only earned three outings.
Falcons director of rugby Dean Richard confirmed the deal on Newcastle's official website and feels the move is beneficial for all parties.
Richards said: "DTH is a proven performer who is well known to Glasgow, he has enjoyed great success up there and this is a move which makes sense for all parties.
"His playing opportunities here at Newcastle have been limited with the huge competition for places we have on the wings, realistically that was going to remain the case going forward but we thank DTH for all of his work on the field and behind the scenes here this season."