Heat the olive oil in a large frying pan on medium-high heat. Season the roast with salt and pepper. Brown the roast on all sides, remove to a plate, and set aside.
In a medium bowl, combine the tomato sauce, Madeira, and garlic. Set aside.
To a slow cooker add the onions and carrots. Add the browned roast and any accumulated juices. Pour the sauce mixture over the top of roast.
Cover and cook on low setting for 8 hours.