The soothsayer makes three brief appearances in the play. In act I, scene 2, he approaches Caesar in the street and bids him "Beware the ides of March," hailing him in a voice which Caesar says is "shriller than all the music." Having heard his message, however, Caesar dismisses the soothsayer as a dreamer.

The soothsayer next appears in act 2, scene 4 at the house of Brutus. Portia questions him, asking if he knows what harm is intended towards Caesar. The soothsayer replies that he does not:

None that I know will be, much that I fear may chance.

He is very insistent, however, that despite the throng around Caesar and despite Caesar's earlier dismissal of his fears, he must continue to warn him.

Finally, at the beginning of III.i, slightly before the assassination, Caesar remarks that that the ides of March have come (the implication being that the soothsayer was wrong, since he is still alive). The soothsayer remarks: "Ay, Caesar, but not gone." There is still time for harm to come to Caesar, as it very soon does.

The presence of the soothsayer and his insistent warnings about matters he barely seems to understand create a sense that Caesar's death is fated. Even as Cassius and Casca are trying to persuade Brutus to join them and thinking of their own conspiracy as a precarious, uncertain enterprise, the soothsayer gives the audience a sense that Caesar's fate is already sealed.