Maternal mental health is a neglected but major global public health challenge, making a substantial contribution to maternal and infant morbidity and mortality. The purpose of this study was to assess the prevalence of common mental disorders and their determinants among pregnant women in the Northwest of Ethiopia. Data were collected from 872 pregnant women residing at the Dabat Demographic and Surveillance Site via an interviewer-administered, standardized questionnaire using an online data kit (ODK) during June–August 2022. A multivariate logistic regression analysis was conducted, and the odds ratio and 95% confidence interval were calculated. Common mental disorders among pregnant women were found to be 13.1% (95% CI: 10.9–15.6). Factors significantly associated with antenatal common mental disorders were marital status (being married, AOR = 2.01 95% CI: 110–3.69), residence (rural, AOR = 2.94 95% CI: 1.72–5.04), family history of common mental disorders (yes, AOR = 4.66 95% CI: 2.09–10.70), unplanned pregnancy (yes, AOR = 1.70 95% CI: 1.02–2.81), and intimate partner violence (yes, AOR = 2.43 95% CI: 1.59–3.73). Common mental disorders are common among pregnant women in the study area, and designing high-quality evidence and interventions that would address the aforementioned factors is vital for the mothers as well as the growth and development of the children.