Major depressive disorder (MDD) has been associated with both all cause and suicide mortality in young adults. However, the effects of parental severe mental disorders (SMDs), such as schizophrenia, bipolar disorder, MDD, alcohol use disorder (AUD), and substance use disorder, on the risks of all-cause and suicide mortality in adolescents and young adults with MDD remain unclear. We retrospectively evaluated the incidence of all-cause and suicide mortality (2001-2011) in 196,000 adolescents (age: 10-17 years) and young adults (age: 18-29 years) with MDD. We investigated associations between parental SMDs and all-cause and suicide mortality among patients with MDD using Cox regression analyses. In addition, we assessed the additive effects of paternal and maternal SMDs on the mortality risk of depressed offspring. Our findings revealed that all cause mortality in offspring was associated with paternal AUD (hazard ratio [HR]: 1.66) as well as maternal schizophrenia (HR: 2.77), bipolar disorder (HR: 1.99), and MDD (HR: 1.25). Furthermore, suicide mortality in offspring was associated with maternal schizophrenia (HR: 4.36) and bipolar disorder (HR: 4.01). Notably, the risk of suicide mortality was the highest in offspring with paternal bipolar disorder and maternal MDD (HR: 7.31). Parental SMDs such as schizophrenia, bipolar disorder, MDD, and AUD are associated with all-cause and suicide mortality in adolescents and young adults with MDD. Optimizing support systems and prioritizing early interventions for parental mental health problems may help reduce the risks of suicide and premature death in young patients with MDD.