In a large Dutch oven over medium heat, melt the butter. Add the onion, carrots, and celery. Cook, stirring occasionally, until the vegetables are softened, about 8–10 minutes.

Stir in the garlic, salt, pepper, and flour. Stir continuously for about 1–2 minutes to coat the vegetables.

Add the chicken broth and wild rice, stirring to combine.

Bring the soup to a boil. Once boiling, reduce the heat to low, cover the pot, and let it simmer gently for 45–50 minutes, stirring occasionally. The wild rice should be tender but still have a slight chew.

Stir in the shredded rotisserie chicken and heavy whipping cream. Let the soup simmer, uncovered, for an additional 5–7 minutes, or just until the chicken is heated through and the soup has thickened slightly. Taste and adjust the salt and pepper if needed.

Serve warm.