Place the chicken breasts in an even layer at the bottom of a 6-quart slow cooker.
In a medium bowl, whisk together the condensed cream of chicken soup, chicken broth, diced onion, thyme, and black pepper.
Pour the soup mixture over the chicken breasts.
Cover and cook on Low for 5 hours.
Remove the chicken from the slow cooker and shred it into 1-inch pieces using two forks.
Return the shredded chicken to the slow cooker and stir in the frozen peas and carrots.
Cut each raw biscuit into 8 equal pieces and place the dough segments in a single layer on top of the chicken mixture.
Cover and cook on High for an additional 60 minutes or until the biscuit dumplings are cooked through and no longer doughy in the center.