Preheat oven to 375 degrees F (190 degrees C) and line a baking sheet with parchment paper.
In a large bowl, mix ground beef, breadcrumbs, eggs, milk, onion, garlic, parsley, basil, salt, and pepper until just combined. Do not overmix.
Form the mixture into a 9x5-inch loaf shape on the prepared baking sheet.
Bake for 40 minutes in the preheated oven.
Remove from oven, pour marinara sauce evenly over the top, and sprinkle with mozzarella and Parmesan cheeses.
Return to oven and bake for an additional 15 to 20 minutes until the internal temperature reaches 160 degrees F (71 degrees C).
Let rest for 10 minutes before slicing and serving.