In a large Dutch oven or stockpot, heat the oil over medium-high heat.
Add the bell pepper, onion, and celery to the pot. Cook, stirring occasionally for approximately 2 minutes.
Add the smoked sausage to the pot to brown, stirring occasionally, for an additional 5 minutes.
Stir in the garlic, diced tomatoes, chicken stock, Cajun seasoning, Old Bay seasoning, salt, and pepper to the pot.
Bring the contents of the pot to a simmer and add the brown rice. Cover.
*Note - if using long grain brown cook covered for 40-45 minutes or until the rice is tender and most of the liquid is absorbed.
*Note - if using instant brown rice, add the rice, cover and turn off heat until the rice is tender and almost all the liquid is absorbed (approximately 10 minutes)
Add the shrimp to the pot (return the heat to medium). Stir and cook covered an additional 5-7 minutes or until the shrimp are pink and opaque.