Heat the olive oil in a large pot or Dutch oven over medium-high heat.
Add the ground beef and cook, breaking it up as it browns, until no longer pink.
Stir in the chopped onion and cook for 3 to 4 minutes, until softened.
Add the chili seasoning, cumin, and garlic powder, and cook for about 30 seconds, until fragrant.
Pour in the Guinness, stirring well and scraping the bottom of the pot to release any browned bits.
Add the diced tomatoes with their juice, the brown sugar, and the kidney beans. Stir to combine.
Bring to a simmer, then reduce the heat to low. Simmer for 20 minutes, stirring occasionally.
Taste and season with salt and pepper as needed.
Serve hot, topped with sour cream and fresh parsley.