No, or at least not yet.
What I believe is that his agent and mother visited Dortmund, training ground and all that, and met with our DoF. This comes from Dortmund's media partner. They and three French sources all claim to have indepent sources that there's sort of an agreement in place between the player's side and Dortmund. This, however, means nothing if the clubs can't agree (hello Ilkay Gündogan).
According to one French guy - who broke the Martial news IIRC - there'll be a meeting this upcoming week to get the clubs on board.
SportBILD, one of Germany's biggest transfer fiction outlets, is the only source that claims it's a done deal.