Our toilet is backed up and water is filled to the brim but there is nothing else in the bowl. I turned off the water supply for the toilet with the little knob connected to the wall, but will the water still be able to drain out of the bowl?
Water usually seeps past most blockages, but not always.
You may have to hand bail the bowl down 1/3 or 1/2. THEN employ a plunger. The older cup plungers worked best with a strong UP pull (hence the bowl draining).
If its a newer, smaller tank, an older cup plunger may not make a tight fit:
This style may work better and will both push and pull against the blockage: