Earlier recognition and accurate assessment of depressive symptoms is important to improving outcomes in individuals with recent-onset schizophrenia spectrum disorders (termed SSD hereafter)—regardless of whether positive psychotic symptoms are present or have resolved. The Montgomery–Åsberg Depression Rating Scale (MADRS) is frequently used to assess depressive symptoms in SSD, but no study has examined the psychometric validity of MADRS scores in individuals exclusively with SSD and sub-grouped by those with and without positive psychotic symptoms. This study involved baseline data from the Psychosis Recent Onset GRoningen Survey (PROGR-S). Measures used were: MADRS, depressive and negative subscales of Positive and Negative Syndrome Scale (PANSSD, PANSSN), and Schedules for Clinical Assessment in Neuropsychiatry (SCAN). The MADRS total score had sufficient concurrent validity with PANSSD (evidence by ρ≥0.70), and insufficient divergent validity with PANSSN (evidenced by ρ ≥0.30), in the full cohort and when sub-grouped by positive psychotic symptoms. In symptom networks, divergent communities comprising either MADRS or PANSSN items were found, except the MADRS item inability to feel overlapped with PANSSN items. The most divergent MADRS items were sadness, pessimism, and suicidal thoughts. The MADRS total score had sufficient predictive validity for determining caseness for MDD based on SCAN, but the optimal cut-off differed in those with and without positive psychotic symptoms (MADRS≥18 versus MADRS≥11). The MADRS has sufficient validity for assessing depressive symptoms in SSD. Since scores might depend upon symptoms of SSD, MADRS≥11 and the presence of sadness, pessimism, or suicidal ideation might be the best indicator of MDD in SSD.