Postpartum depression (PPD) has detrimental effects on the health of the mother, child and family. Socio-demographic variables can influence PPD. Sense of coherence (SOC) is a personal resource that mitigates the experience of stressful events. We hypothesized that SOC would have a protective effect against PPD over time. The aim was to investigate the effects of socio-demographic factors and SOC on PPD at birth (T1) and nine months postpartum (T2). A longitudinal study of primiparous women (n = 114; age range 18–47 years) measured PPD, SOC and socio-demographics at T1 and T2. The majority were married, had no economic difficulties and were employed before birth. Results showed that PPD at T1 (15.8%) declined to 6.2% (T2). Job status was positively associated with SOC at T1. The structured equation model accounted for 27% of the variance in PPD (T2). In the first pathway, job status was linked to PPD (T2) via SOC at T1 and T2. In the second, SOC and PPD (T1) and SOC (T2) mediated the link between job status and PPD (T2). Results and clinical implications are discussed in the context of the theory of conservation of resources. An intervention for enhancing SOC is recommended for woman at risk of PPD.