Spray the inside of your slow cooker lightly with nonstick cooking spray for easier cleanup, or use a slow cooker liner if you prefer.
In a small bowl, stir together the barbecue sauce and brown sugar until the sugar is mostly dissolved and the sauce looks glossy and slightly thicker.
Add a thin layer of the BBQ sauce mixture to the bottom of the slow cooker. Arrange the ribs in the slow cooker in an even layer; it’s fine if they overlap slightly, but try not to stack them too high so they cook evenly.
Pour the remaining BBQ sauce mixture evenly over the ribs, turning them with tongs to make sure every piece is well coated. Spoon some sauce from the bottom over any spots that look dry.
Cover the slow cooker with the lid and cook on LOW for 7–8 hours, or on HIGH for 3 1/2–4 hours, until the ribs are very tender and easily pull apart with a fork.
Once the ribs are cooked and tender, preheat your oven broiler to high and line two rimmed baking sheets or foil trays with aluminum foil for easy cleanup.
