Precast concrete (PC) can potentially improve construction industry projects when used as a primary process in the precast concrete supply chain (PCSC). Successful inventory reduction and on-time delivery are essential in the PCSC because of critical scheduling and cost factors. To solve these challenges, this study applied Just-In-Time (JIT) strategies in the PCSC using the Discrete-Event Simulation (DES) model to help manufacturers identify the optimal decision. The factors considered were offsite inventory levels (based on days buffered) and batch delivery decisions that reduced supply penalties and improved construction performance. The model was validated based on a precast project experiment in Vietnam; the model provided a saving of 52% in manufacturer penalties and reduced construction idle work by 77%. An optimal combined decision was provided for the manufacturer, such as a 1day-4batch decision with maximum benefit and a 2day-2batch decision for safety using an uncertainty risk consideration in the PC wall panel study case. This research contributes a tool to help manufacturers in decision making and promotes the use of JIT applications/strategies in the PCSC process.