Place onion, bell peppers, garlic, mushrooms, crushed tomatoes, tomato paste, broth, wine, and seasonings in the crockpot; stir to combine.
Nestle chicken thighs into the sauce, turning to coat and seasoning lightly with salt and pepper.
Cook on low for 6–7 hours or high for 3–4 hours, until chicken is tender and internal temp reaches 165°F.
Remove chicken to a platter, shred or keep whole, then stir sauce and adjust seasoning.
Return chicken to sauce to warm briefly, sprinkle with parsley, and serve over pasta, rice, or mashed potatoes.