An occupant restraint system includes a rollover prediction unit, a rollover detection unit, primary and secondary pre-tensioner units, and a control unit. The rollover prediction unit is configured to predict a rollover of the vehicle based on a state of the vehicle. The rollover detection unit is configured to detect a rollover of the vehicle based on the state of the vehicle. The primary and secondary pre-tensioner units are configured to apply a tension to a seat belt so as to restrain an occupant in a seat. An operation force of the secondary pre-tensioner unit is stronger than that of the primary pre-tensioner unit. The control unit is configured to activate the primary pre-tensioner unit based on a prediction by the rollover prediction unit that a rollover occurs and activate the secondary pre-tensioner unit based on a detection by the rollover detection unit that the rollover occurs.