Cut chicken breasts into bite-sized chunks approximately one-inch square. Pat dry with paper towels to ensure even browning and cooking throughout. Place prepared chicken into your slow cooker's bottom layer, creating a foundation for other ingredients.

Add diced potatoes, carrots, celery, onion, and minced garlic directly into the slow cooker with the chicken. Layer these vegetables evenly to ensure uniform cooking. Stir tomato paste into the chicken broth until fully combined, then pour this mixture over everything.

Season with dried thyme, dried rosemary, bay leaf, salt, and black pepper. Stir well to distribute seasonings evenly throughout the mixture. Cook on low setting for 6 hours, allowing the chicken to become incredibly tender and all flavors to meld beautifully.

After 6 hours, your cozy slow cooker chicken stew should be fragrant and vegetables tender when pierced with a fork. Remove the bay leaf carefully before the next step. Taste and adjust seasonings with additional salt and pepper as needed for your preference.

In a small bowl, whisk together cornstarch and water until no lumps remain. Slowly stir this slurry into the slow cooker while gently stirring the stew. Continue cooking for 15-20 minutes until the broth thickens into a silky sauce.

Ladle the stew into bowls and serve immediately while still steaming hot. The slow cooker chicken stew keeps beautifully warm on the warm setting for up to two hours if you're eating in shifts. This makes it perfect for families with staggered schedules and quiet evenings.