<p>Couple’s relationship can be either a protective or a risk factor for perinatal mental health, with an expectably higher impact on mothers and fathers facing adversity. This study analyzed the association between couple’s relationship before the COVID-19 pandemic and mother’s and father’s postnatal depressive and anxiety symptoms during a major adversity condition, the COVID-19 pandemic. A sample of 108 primiparous mothers and fathers was recruited and assessed at the first trimester of pregnancy before the COVID-19 pandemic and assessed again at six months postpartum, before (<i>n</i> = 68) or during the COVID-19 pandemic (<i>n</i> = 40). At both assessment waves, mothers and fathers completed self-reported measures of positive and negative dimensions of the couple’s relationship and depressive and anxiety symptoms. The positive dimension of the couple’s relationship before the COVID-19 pandemic was associated with less postnatal depressive symptoms in mothers and fathers facing the COVID-19 pandemic, while no association was found in mothers and fathers who did not face the COVID-19 pandemic. Couple’s relationship before the COVID-19 pandemic may be a protective factor for postnatal depressive symptoms in mothers and fathers facing the COVID-19 pandemic, and thus may promote postnatal mental health in parents facing adversity.</p>