Preheat the oven to 325 degrees F (165 degrees C). Grease a 3-quart baking dish.
Cut bread into 3/4-inch cubes and spread into a single layer on the prepared baking sheet.
Bake in the preheated oven until crisp, 12 to 17 minutes.
Meanwhile, heat olive oil in a large skillet over medium heat. Add onions and celery; cook and stir until soft, 8 to 10 minutes. Stir in sage, thyme, salt, and pepper.
Add toasted bread cubes, chicken broth, and beaten eggs to the skillet. Stir until well combined, then transfer mixture to a greased 3-quart baking dish.
Cover and bake in the preheated oven for 30 minutes. Uncover and continue baking until the top is crisp and lightly browned, about 10 more minutes.