Season chicken with salt and pepper. In a large skillet, heat oil over medium-high. In batches, cook chicken, skin side down, until skin is golden brown, about 4 minutes.
Combine onion, garlic, and thyme in a 5-to-6-quart slow cooker and season with salt and pepper. Top with chicken, skin side up, in a tight layer. In a small bowl, whisk together wine and flour until smooth and add to slow cooker.
Cover and cook on high until chicken is tender, about 3 ½ hours (or 7 hours on low).
Cook couscous according to package instructions. Serve chicken and sauce over couscous, sprinkled with parsley.
