Near-room-temperature liquid metals offer unique and crucial advantages over solid metals for a broad range of applications which require soft, stretchable and/or reconfigurable structures and devices. In particular, gallium-based liquid metals are the most suitable for a wide range of applications, not only owing to their low melting points, but also thanks to their low toxicity and negligible vapor pressure. In addition, gallium-based liquid metals exhibit attractive optical properties which make them highly suitable for a variety of photonics applications. This review summarizes the material properties of gallium-based liquid metals, highlights several effective techniques for fabricating liquid-metal-based structures and devices, and then focuses on the various photonics applications of these liquid metals in different spectral regions, following with a discussion on the challenges and opportunities for future research in this relatively nascent field.