We advance a new account of why people endorse conspiracy theories, arguing that individuals use the social–cognitive tool of projection when making social judgements about others. In two studies, we found that individuals were more likely to endorse conspiracy theories if they thought they would be willing, personally, to participate in the alleged conspiracies. Study 1 established an association between conspiracy beliefs and personal willingness to conspire, which fully mediated a relationship between Machiavellianism and conspiracy beliefs. In Study 2, participants primed with their own morality were less inclined than controls to endorse conspiracy theories – a finding fully mediated by personal willingness to conspire. These results suggest that some people think ‘they conspired’ because they think ‘I would conspire’.