Mix thyme, salt, and black pepper in a small bowl and rub the mixture over both sides of brisket.
Heat olive oil in a roasting pan over medium-high heat; place brisket in the hot oil and brown on both sides, 3 to 4 minutes per side. Remove brisket from pan and set aside.
Place red onion slices into the hot roasting pan and cook and stir until onion is slightly softened, about 2 minutes. Stir in beef broth, tomato sauce, and wine.
Place the brisket back into the roasting pan and cover pan with foil.
Roast the brisket in the preheated oven for 1 hour; remove foil and baste brisket with pan juices. Place foil back over roasting pan and roast brisket until very tender and pan sauce has thickened, 1 1/2 to 2 more hours.
