Wash and pat dry your chicken thighs. Then trim off the excess fat.
Mix onion powder, garlic powder, dried thyme, dried oregano, sage, black pepper, cayenne pepper, mustard powder, paprika, celery seeds, and salt in a small bowl until well combined.
Rub chicken thighs with seasoning so they are well coated.
Let it rest in the refrigerator for about 30 minutes (overnight is even better) to allow the flavors to penetrate the chicken.
When you’re ready to start smoking, remove the thighs from the refrigerator and let them sit at room temperature for about 10 minutes before smoking. (This allows for more even cooking.)
Fill your pellet grill’s hopper with your preferred wood pellets, such as apple wood or hickory.
Preheat it to 225°F (107°C). This may take 10-15 minutes. Lightly oil the grates so the chicken doesn’t stick.
Place the thighs directly on the preheated grill grates. Close the lid and smoke the chicken thighs for about 60-90 minutes, or until the thickest portion reaches 165℉/75℃. (Flip them once during smoking if you’d like.)
Optionally, brush the thighs with barbecue sauce during the last 10-15 minutes of smoking. You could also brush them after the chicken is done.
Once the chicken thighs have reached the desired internal temperature, take them off the grill and transfer them to a plate.
Tent the meat loosely with aluminum foil and let it rest for 10 minutes so the juices can redistribute for tenderer, juicier chicken.
Serve with your favorite sides, and enjoy!