In the Internet of Things era, flexible and wearable gas sensors are increasingly vital for real‐time monitoring in healthcare, environmental safety, and industrial security. These sensors detect hazardous gases at room temperature and seamlessly integrate with clothing and portable devices. The 2D materials, including transition metal dichalcogenides, black phosphorus, MXenes, graphene and its derivatives, and metal–organic frameworks, stand out due to their exceptional electrical, mechanical, and physicochemical properties, such as large surface areas, high carrier mobility, and intrinsic flexibility. This review summarizes recent advancements in designing, fabricating, and applying 2D‐material‐based flexible gas sensors. It highlights how engineering approaches like defect creation, composite formation, and surface functionalization significantly enhance sensor sensitivity, selectivity, and response times. Comparative performance data across various material families are presented, alongside effective strategies for integrating 2D materials onto diverse flexible substrates such as polymers, textiles, and paper, emphasizing durability under mechanical stress. The review critically addresses current challenges, including large‐scale manufacturing, long‐term stability, and interference from ambient humidity. Furthermore, it explores innovative solutions like self‐healing sensors, artificial intelligence‐driven sensor arrays, in situ surface passivation, and multisensor platforms coupled with machine learning algorithms, offering valuable insights for advancing next‐generation wearable gas‐sensing technologies.

2D metal sulphides (MSs) have attracted enormous amounts of attention in developing high‐performance gas sensors. 2D noble metal sulphides and their derivatives, however, have been less studied due to their predominant nonlayered crystal structures for inefficient exfoliation, despite their surface and peculiar optoelectronic properties. Herein, we successfully synthesize 2D palladium sulphate (PdSO₄) from palladium sulphide (PdS) bulk crystals by liquid‐phase exfoliation, in which the presence of oxygen species in the exfoliation solvent plays a key role in the sulphate transformation. Ultrathin 2D PdSO₄planar nanosheets, with thicknesses of ≈3 nm and submicrometer lateral dimensions, exhibit a broad absorption across the visible spectrum, a narrow bandgap of ≈1.35 eV, and a nanosecond scaled long exciton lifetime, which are all suitable for the visible‐light‐driven optoelectronic gas sensing applications. The 2D PdSO₄‐based sensor demonstrates a reversible, selective, and sensitive response toward ppb‐leveled NO₂gas at blue light irradiation, featuring a response factor of ≈3.28% for 160 ppb NO₂, a low limit of detection of 1.84 ppb, anda > 3 times response factor enhancement over other gases. Herein, the possibility of realizing 2D ultrathin noble metal sulphide compounds from their nonlayered crystal structures and strong potentials in developing high‐performance chemical sensors is explored.