The ability to accurately assess others’ intents, beliefs, and emotions – called Theory of Mind (ToM) – is conjectured to be important for social cooperation. We study the role of ToM ability in fostering cooperation in the simultaneous and sequential prisoners dilemma (PD) games. Our norm-based model predicts that high ToM ability individuals will believe in more cooperation and cooperate at higher rates than low ToM ability individuals in the sequential PD game relative to the simultaneous PD game. Experimental results match these predictions and reveal that ToM ability affects cooperation via beliefs in others’ cooperativeness rather than fixed preference traits