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Optical anisotropy is a key element to control the polarization of light in polarizing optics, light modulators, imaging and communication systems. While artificial form birefringent architectures can possess larger optical anisotropy than natural anisotropic crystals, their deployment is limited by the demanding fabrication. We demonstrate the realization of giant optical anisotropy via engineering the polarizability tensor in a natural material, BaTiS₃, which has a highly anisotropic quasi-1D structure and features easily accessible in-plane anisotropy. We report the observation of a large, broadband infrared birefringence and linear dichroism. As-grown crystals demonstrate strong dichroism with two distinct optical absorption edges for linear polarization along two crystallographic directions. The birefringence magnitude of BaTiS₃ is compared with various widely used natural anisotropic crystals.