Across four studies, we test the hypothesis that people exhibit “slippery slope” thinking in their judgments of moral character—that is, do observers judge that a person who behaves immorally will become increasingly immoral over time? In Study 1, we find that a person who commits an immoral act is judged as more likely to behave immorally and as having a worse character in the future than in the past. In Study 2, we find that it is the commission of an immoral act specifically—rather than merely attempting an immoral act—that drives this slippery slope effect. In Study 3, we demonstrate that observers judge the moral agent as more likely to commit acts of greater severity further in time after the initial immoral act. In Study 4, we find that this effect is driven by an anticipated corrupting of moral character, related to perceptions of the agent’s guilt.