Combine Ingredients: In a large stockpot, combine water, salt, brown sugar, peppercorns, bay leaves, thyme, sage, rosemary, onion, and garlic. Bring to a boil, stirring until the salt and sugar are dissolved.
Cool the Brine: Let the brine cool completely before using.
Prepare the Turkey: Rinse the turkey inside and out with cold water. Pat dry with paper towels.
Brine the Turkey: Place the turkey in a large, food-safe container or a large, clean garbage bag. Pour the cooled brine over the turkey, ensuring it is completely submerged. If needed, add more cold water to cover the turkey.
Refrigerate: Refrigerate the brined turkey for 18 hours.
Rinse and Roast: Remove the turkey from the brine and rinse thoroughly with cold water. Pat dry with paper towels.