A death rate of approximately 32.7 in 100,000 traffic injury victims was reported in Thailand. The prediction of early death would identify and enable prioritization of the most severe patients for resuscitation and consequently reduce the number of deaths. This study aimed to develop a clinical prediction scoring system for 24 h mortality in adult major trauma patients. Retrospective-prognostic clinical prediction was applied in the case of 3173 adult trauma patients who were classified into three groups: death within 8 h, death between 8 and 24 h, and alive at 24 h. The predictors were obtained by univariable and multivariable logistic regression, and the coefficient of parameters was converted to predict early death. The numbers of patients who died within 8 h and between 8 and 24 h were 46 (1.5%) and 123 (3.8%), respectively. The predictors included systolic blood pressure <90 mmHg, heart rate ≥120 bpm, Glasgow coma scale ≤8, traffic injury, and assault injury. The scores of 4 indicated a mortality rate of 12% with a high specificity of 0.89. The suggested TERMINAL-24 scoring system can be used for the prediction of early death in the Emergency Department. However, its discrimination ability and precision should be validated before practical use.