We describe an approach for real-time Studies of the transition-state dynamics of charge-transfer reactions. An application to the bimolecular reaction of benzene with iodine is reported. The measured 750+/-50 fs transient growth of the free I atom product elucidates the nature of the transition state and the mechanism for the dissociative charge-transfer reaction. The mechanism is formulated in relation to the impact geometry and the dative bonding, which are crucial to condense-phase and surface reactions, and is supported by molecular dynamics.