Synchrony among the senses lies at the heart of our possession of a unified conscious perception of the world. However, due to discrepancies in physical and neural information processing from different senses, the brain accommodates a limited range of temporal asynchronies between sensory inputs, i.e. the multisensory temporal binding window (TBW). Using non-invasive brain stimulation, we sought to modulate the audio-visual TBW and to identify cortical areas implicated in the conscious perception of multisensory synchrony. Participants performed a simultaneity judgment task while experiencing anodal (Experiment 1) or cathodal (Experiment 2) transcranial direct current stimulation (tDCS) over parietal and frontal regions. The results demonstrate that stimulating the right posterior parietal cortex significantly reduces the audio–visual TBW by approximately 30%, thereby causally linking this region to the plasticity of the TBW. This highlights a potential interventional technique for populations with a wider TBW, such as in autism and dyslexia.