I would say no. The free night certificate as indicated is for you only.

However, in theory, you could try to book a room (by phone) for yourself and add a second person as "Guest #2." Indicate that you will be using a free night cerificate. Get Marriott to send an e-mail confirmation to you which will show your name and the other Guest's name.

You may want to ask Marriott if the other person can bring the free night certificate to check-in since both of your names are on it. (Hypothetically, both of you could be traveling to the hotel at separately). If the reservationst says yes, then okay. If not, then you may just want to use it yourself.