Objective The staging and management of patients with newly diagnosed non-small cell lung cancer (NSCLC) in the setting of recently diagnosed other (metachronous or synchronous) primary cancer are challenging. This retrospective cohort study was conducted to test our hypothesis that baseline FDG PET/CT parameters, including whole-body metabolic tumor volume (MTVWB), total lesion glycolysis (TLGWB) and maximum standardised uptake value (SUVmaxWB) are associated with overall survival (OS) of such patients. Materials and Methods A total of 110 NSCLC patients (52 men and 58 women, aged 68.6 ± 7.8 years) with other primary malignant cancers who had baseline FDG PET/CT scans were retrospectively reviewed. MTVWB, TLGWB and SUVmaxWB were measured. Kaplan-Meier analysis with the log-rank test and Cox regression models were used to assess the association of OS with FDG PET/CT parameters and clinical risk factors. Results Kaplan-Meier analysis and univariate Cox regression models demonstrated significant associations of OS with ln(MTVWB), ln(TLGWB), ln(SUVmaxWB), TNM stage, and treatment type (surgery versus no treatment). Multivariable Cox regression models showed a significant relationship of OS with ln(MTVWB) (HR = 1.368, P = 0.001), ln(TLGWB) (HR = 1.313, P < 0.001) and ln(SUVmaxWB) (HR = 1.739, P = 0.006), adjusted for age, treatment type, tumor histology, and TNM stage. TNM stage was not significantly associated with OS when MTVWB, TLGWB or SUVmaxWB were included in the multivariable models. Conclusion MTVWB, TLGWB, and SUVmaxWB from baseline FDG PET/CT are individually associated with OS of patients with both NSCLC and other primary malignant tumors; independent on age, treatment type, tumor histology and TNM stage.