Heat the olive oil in a large pot over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Add the diced onion and minced garlic to the pot. Cook for 3 minutes until the onion softens.
Stir in the cubed russet potatoes, sweet potato, and sliced parsnips. Cook for 2 minutes while stirring.
Add the diced tomatoes, tomato paste, beef broth, dried thyme, salt, and black pepper. Stir everything together.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 30 minutes, stirring occasionally, until the vegetables are tender.
Taste and adjust salt or pepper if needed before serving.