The young midfielder is currently with Sparta Rotterdam and still has one year remaining on his present deal.
But he has concurred on a four-year contract with NAC, which he will sign on Friday providing he passes a medical.
Back in the spring, Mendes da Silva's displays for Sparta caught the eye of City and Boro but the Premiership pair declined to follow up their interest.
Mendes da Silva joins NAC as a replacement for Csaba Feher (pictured), who joined PSV Eindhoven earlier this week.
