Heat the olive oil in a large pot or Dutch oven over medium heat.
Add the diced onion and sauté for about 3-4 minutes until it becomes translucent.
Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the chicken pieces to the pot and cook until they are no longer pink on the outside, about 5-6 minutes.
Add the sliced mushrooms, carrots, and celery to the pot and cook for another 5 minutes.
Pour in the chicken broth and add the dried thyme, dried rosemary, salt, and black pepper. Stir to combine.
Bring the stew to a gentle boil, then reduce the heat to low and let it simmer for 30 minutes, stirring occasionally.
Taste and adjust seasoning if necessary. If you prefer a thicker stew, let it simmer uncovered for an additional 5-10 minutes.
Serve hot, garnished with fresh parsley.