Sensory-guided actions entail the processing of sensory information, generation of perceptual decisions, and the generation of appropriate actions. Neuronal activity underlying these processes is distributed into sensory, fronto-parietal, and motor brain areas, respectively. How the neuronal processing is coordinated across these brain areas to support functions from perception to action remains unknown. We investigated whether phase synchronization in large-scale networks coordinate these processes. We recorded human cortical activity with magnetoencephalography (MEG) during a task in which weak somatosensory stimuli remained unperceived or were perceived. We then assessed dynamic evolution of phase synchronization in large-scale networks from source-reconstructed MEG data by using advanced analysis approaches combined with graph theory. Here we show that perceiving and reporting of weak somatosensory stimuli is correlated with sustained strengthening of large-scale synchrony concurrently in delta/theta (3–7 Hz) and gamma (40–60 Hz) frequency bands. In a data-driven network localization, we found this synchronization to dynamically connect the task-relevant, that is, the fronto-parietal, sensory, and motor systems. The strength and temporal pattern of interareal synchronization were also correlated with the response times. These data thus show that key brain areas underlying perception, decision-making, and actions are transiently connected by large-scale dynamic phase synchronization in the delta/theta and gamma bands. Author Summary We studied the functional role of interareal phase synchronization in the perception-to-action cascade. To this end we recorded human cortical activity with magnetoencephalography (MEG) during a task where weak somatosensory stimuli were perceived or remained unperceived. We identified time-resolved large-scale networks of synchronization by using source-reconstructed MEG data with advanced analysis tools and graph theory. We found that perceiving and reporting of weak somatosensory stimuli was correlated with sustained strengthening of large-scale phase synchronization concurrently in delta/theta (3–7 Hz) and gamma (40–60 Hz) frequency bands. Synchronization characterizing the perceived stimuli connected the sensorimotor system with frontoparietal attentional systems. These data suggest that large-scale network synchronization may coordinate neuronal processing across brain regions during perception, decision-making, and when responding to weak somatosensory stimuli.