In a bowl, combine garlic and onion powder, thyme, oregano, sage, black pepper, salt, cayenne pepper, mustard powder, paprika, and celery seeds until fully combined. Set aside.
Rinse and pat dry your chicken with paper towels.
Generously coat the chicken with the spice mix, making sure every inch is covered. Let it sit tightly covered in the refrigerator for about an hour or up to 24 hours for the flavors to penetrate. Let your chicken come to room temperature before smoking.
When ready to smoke, preheat your smoker to 225°F (110°C) according to your manufacturer's instructions. If you're using a charcoal grill, arrange the charcoal to one side to create a hot side and a cooler side. If using a pellet grill, double-check the hopper and make sure it has enough pellets.
Lightly oil your grill grates and then place your chicken directly on the grill grates.
Close your smoker and smoke for 2-3 hours covered, about 30 to 45 minutes per pound. The internal temperature of your chicken should reach 165°F.
Remove the chicken from the grill and let it rest for about 15-20 minutes. This will enable the juices inside the chicken to become evenly distributed.
Then, using two forks, begin shredding the chicken apart into bite-sized pieces.
You can serve the smoked pulled chicken hot as a main dish or use it to make sandwiches, tacos, or salads.