Lightly grease the inside of the slow cooker to prevent sticking.
Arrange the chicken in a single, even layer at the bottom.
Mix cranberry sauce, chicken broth, brown sugar, Dijon mustard, onion soup mix, garlic powder, and black pepper until smooth.
Pour the sauce over the chicken, making sure all pieces are well coated.
Cover and cook on LOW for 6 to 7 hours or HIGH for 3 to 4 hours until the chicken reaches 165°F.
For a softer texture, shred the chicken during the last 20 to 30 minutes and return it to the sauce.
Adjust seasoning if needed, then serve hot with extra sauce spooned over the top.