Place the sliced onion in the bottom of the slow cooker to create a base layer.
Arrange the chicken thighs on top of the onion in a single layer.
In a small bowl, stir together the minced garlic, diced tomatoes with their juice, artichoke hearts, olives, olive oil, oregano, thyme, salt, and pepper.
Pour the tomato mixture evenly over the chicken thighs.
Cover and cook on low for 6 hours or on high for 3 hours, until the chicken is very tender.
Sprinkle the chopped parsley over the chicken before serving.