In a mixing bowl, whisk together the maple syrup, Dijon mustard, minced garlic, chicken broth, dried thyme, salt, and black pepper until smooth.
Place the chicken thighs in the bottom of the slow cooker and pour the sauce mixture over them.
Add the halved Brussels sprouts around and on top of the chicken.
Cover and cook on low for 6 to 7 hours until the chicken is tender and the Brussels sprouts are soft.
Stir gently before serving to coat everything in the sauce.