Brown the sausage: Heat a large skillet over medium heat. Add the sausage and cook, breaking it into crumbles.
Add the vegetables: When the sausage is about halfway cooked, add the diced onion and garlic. Continue cooking until the sausage is fully cooked and the onion is tender.
Drain: Carefully drain the excess grease, then return the sausage mixture to the skillet.
Add the cheese and Rotel: Stir in the undrained Rotel, cubed Velveeta, and black pepper.
Melt: Reduce the heat to low and cook, stirring frequently, until the cheese is completely melted and the dip is smooth and well combined.
Serve: Serve hot with tortilla chips, corn chips, or fresh vegetables for dipping.