Heat the olive oil in a large skillet over medium-high heat. Add the venison cubes and cook for about 10 minutes, turning regularly, until it is browned on all sides.
Transfer the venison to a slow cooker. Add the garlic, onions, green pepper, carrots, rosemary, thyme, paprika, salt, and black pepper.
In a small bowl, whisk together the Worcestershire sauce, beef broth, tomato paste, and red wine. Pour this mixture into the slow cooker.
Cover and cook on low for 6-8 hours or on high for 4-6 hours.
Once the backstrap is cooked through, stir in the cornstarch and cook on high for an additional 15 minutes or until the sauce thickens.
Serve the venison backstrap over mashed potatoes or with a side of cooked noodles. Enjoy!