A versatile and ultra-sensitive sensor platform based on lamellar Ti3C2Tx (MXene)-modified glassy carbon electrode has been developed for the detection of bromate (BrO3−) in water. MXene showed unique electrocatalytic properties towards effective BrO3− reduction and the developed sensor displayed a linear response for the BrO3− concentration from 50 nM to 5 $\mu$M with a detection limit of 41 nM. The catalytic reduction of BrO3− by MXene was assumed by an increase of the peak current and a shift to lower potential. Surface changes to MXene after electrocatalytic reduction of BrO3− was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formation of trace TiO2 crystals at the surface of Ti3C2Tx during the electrochemical reduction of BrO3− have confirmed the redox reaction between BrO3− and MXene. Also the developed sensor showed excellent selectivity for BrO3− among other interfering ions. This work provides an evidence for the application of MXene as an effective platform for detection of water contaminants especially when its redox functionality can be utilized.