Preheat an oven to 350 degrees F (175 degrees C). Grease a 9x5-inch loaf pan.
Beat together the cream cheese, sugar, butter, eggs, and banana in a large bowl until very smooth. Stir in the flour, baking powder, baking soda, and walnuts until just combined. Pour the batter into the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour and 15 minutes. Cool in the pan for 10 minutes before removing to cool completely on a wire rack.