Heat a little oil in a large pot or Dutch oven over medium-high heat. Add the ground beef and cook until browned, lightly seasoning it with salt and black pepper.
Add the diced onion and drained Rotel. Continue cooking until the onion begins to turn translucent and fragrant.
Add the corn, black beans, pinto beans, taco seasoning, and ranch seasoning. Stir briefly to combine, then pour in the chicken broth.
Lower the heat to a simmer and cook for about 20 minutes, stirring occasionally.
Add the cubed Velveeta, then turn off the heat. Let the cheese sit in the hot soup for a few minutes to begin melting.
Stir until the Velveeta is completely melted and incorporated into the soup, then serve.