The S-QoL 18 is a self-administered questionnaire that assesses quality of life (QoL) among individuals with schizophrenia. This study aims to validate the S-QoL 18 in bipolar and depressive disorders for a more widespread use in psychiatric settings. This study was conducted in a non-selected sample of individuals with bipolar and depressive disorders in the day hospital of a regional psychiatric academic hospital. Two-hundred and seventy-two stable outpatients with bipolar ( = 73) and recurrent and persistent depressive ( = 199) disorders were recruited over a 12 month-period. The S-QoL 18 was tested for construct validity, reliability, and external validity. The eight-factor structure of the S-QoL 18 was confirmed by confirmatory factor analysis (RMSEA = 0.075 (0.064-0.086), CFI = 0.972, TLI = 0.961). Internal consistency and reliability were satisfactory. External validity was confirmed via correlations between S-QoL 18 dimension scores, symptomatology, and functioning. The percentage of missing data for the eight dimensions did not exceed 5%. INFIT statistics were ranged from 0.7 to 1.2, ensuring that all items of the scale measured the same QoL concept. In conclusion, the S-QoL 18 appears to be a valid and reliable instrument for measuring QoL in patients with bipolar and depressive disorders. The S-QoL 18 may be used by healthcare professionals in clinical settings to accurately assess QoL in individuals with bipolar and depressive disorders, as well as in schizophrenia.