The development of efficient catalysts with a large number of active sites, tunable bandgap, and large surface area has been very challenging. In addition, a significant bottleneck in the application of catalysts for water treatment is their dissolution under extreme conditions, such as highly acidic or highly alkaline conditions that lead to poor application of the reported materials in real‐world applications. In this study, the lanthanum (La)‐doped molybdenum disulfide (MoS2) nanosheets are reported for efficient breakdown of toxic pollutants from wastewater under a wide pH range from strongly alkaline to strongly acidic solutions. The La‐MoS2 nanosheets (NSs) are prepared by a facile hydrothermal approach using a two‐step methodology. A redshift is observed upon La doping, indicating that the bandgap is lowered after La doping in MoS2. The changes in bandgap and electronic structure are further investigated using the density functional theory (DFT), which reveal that doping of La introduces new states within the bandgap region, allowing for further induced energy transitions. The La‐MoS2, having a doping concentration of 2%, exhibits the highest catalytic activity against methylene blue (MB) in neutral, acidic, and alkaline solutions, as well as substantial inhibitory activity for bacterial strains such as Escherichia coli (E. coli). In summary, the modified catalyst provides a pathway to design highly efficient catalysts for all pH range water treatment as well as good activity against microbes.