Place chicken in the bottom of the slow cooker. Top with frozen vegetables, onion, and garlic.
In a small bowl, whisk together cream of chicken soup, chicken broth, thyme, salt, and pepper. Pour over the chicken and vegetables.
Cover and cook on low for 6–7 hours or on high for 3–4 hours, until the chicken is tender.
Remove the chicken, shred it with two forks, and return it to the slow cooker.
Stir in the heavy cream and cook for an additional 15–20 minutes to heat through.
Meanwhile, bake the refrigerated biscuits according to package directions.
Serve the chicken pot pie mixture topped with a warm biscuit.