Cook bacon in a large, deep skillet over over medium-high heat until evenly browned, 5 to 10 minutes. Remove from the skillet, crumble and set aside. Brown stew meat in bacon grease for flavor.
Put onion, brown sugar, vinegar, cumin, chili powder, garlic, mustard, ketchup, salt, and pepper in slow cooker and mix well. Add bacon and venison and stir together.
Cook on Low for at least 8 hours. Use a fork to separate the meat into a thick and yummy Sloppy Joe-style barbecue.