Thought insertion (TI) is characterized by the experience that certain thoughts, occurring in one’s mind, are not one’s own, but the thoughts of somebody else and suggestive of a psychotic disorder. We report a robotics-based method able to investigate the behavioural and subjective mechanisms of TI in healthy participants. We used a robotic device to alter body perception by providing online sensorimotor stimulation, while participants performed cognitive tasks implying source monitoring of mental states attributed to either oneself or another person. Across several experiments, conflicting sensorimotor stimulation reduced the distinction between self- versus other-generated thoughts and was, moreover, associated with the experimentally generated feeling of being in the presence of an alien agent and subjective aspects of TI. Introducing a new robotics-based approach that enables the experimental study of the brain mechanisms of TI, these results link TI to predictable self-other shifts in source monitoring and specific sensorimotor processes.