Add diced onion, cream of celery soup, cream of chicken soup, parsley, poultry seasoning, black pepper, and chicken breasts to the crockpot.
Pour in the chicken broth and mix gently to combine. Cover and cook on low for 5 hours or until the chicken is tender.
Remove the chicken, shred it using two forks, and return it to the crockpot.
Stir in the thawed frozen vegetables and mix well.
Cut the refrigerated biscuits into small bite-sized pieces and add them to the crockpot.
Cover and cook on high for 1 hour, stirring occasionally, until the biscuits are fluffy and cooked through.
Garnish with fresh parsley and serve warm.
Enjoy your creamy, comforting crockpot chicken and dumplings!