can the qazi, who is conducting the nikah of a person, and who is well known to this person, also act as one of the two witnesses of this nikah?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The jurists stated that the testimony of a person is not valid for his own self. Therefore, if the Ma’athoon (the marriage registrar) conducts the marriage contract in a way that he is one of the two contracting parties (i.e. he is deputized by either party), then it is not permissible for him to be one of the two witnesses to the marriage contract, because, in this case, he would be a witness to what he himself has done.

As-Saawi from the Maaliki School of jurisprudence, said: “The testimony of a Mutawalli (trustee of an endowment and the like) is not valid because it is a testimony of what he himself has done.”

The fact that the husband knows him or does not know him does not change the ruling.

On the other hand, if he is just authenticating the marriage, then it is permissible to consider him as a witness.

Allaah Knows best.