Place the chicken thighs into the slow cooker. Add sliced carrots, chopped celery, diced onion, minced garlic, dried thyme, and pour in the chicken broth.
Cover and cook on low for 6-8 hours, until the chicken is fall-apart tender and the vegetables are soft.
Remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken to the soup.
Stir in chopped fresh parsley and adjust the seasoning with salt, pepper, and a squeeze of lemon or vinegar if desired.
Ladle the hot soup into bowls, ensuring each serving has plenty of chicken and vegetables. Garnish with extra parsley if desired.
Enjoy your cozy, nourishing chicken soup with crusty bread or your favorite sides.