Background Depression in pregnancy (antenatal depression) in many low and middle-income countries is not well documented and has not been given priority for intervention due to competing urgencies and the belief that it does not immediately cause fatalities, which mainly emanated from lack of comprehensive research on the area. To fill this research gap, this systematic review was conducted to investigate the burden of antenatal depression and its consequences on birth outcomes in low- and middle-income countries. Methods We systematically searched the databases: CINHAL, MEDLINE, EMCare, PubMed, PSyc Info, Psychiatry online, and Scopus for studies conducted in low and middle-income countries about antenatal depression and its association with adverse birth outcomes. We have included observational studies (case control, cross-sectional and cohort studies), written in English-language, scored in the range of good quality on the Newcastle Ottawa Scale (NOS), and were published between January 1, 2007 and December 31, 2017. Studies were excluded if a standardized approach was not used to measure main outcomes, they were conducted on restricted (high risk) populations, or had fair to poor quality score on NOS. We used Higgins and Egger's to test for heterogeneity and publication bias. Primary estimates were pooled using a random effect meta-analysis. The study protocol was registered in PROSPERO with protocol number CRD42017082624. Result We included 64 studies (with 44, 035 women) on antenatal depression and nine studies (with 5,540 women) on adverse birth outcomes. Antenatal depression was higher in the lower-income countries (Pooled Prevalence (PP) = 34.0%; 95%CI: 33.1%-34.9%) compared to the middle-income countries (PP = 22.7%, 95%CI: 20.1%-25.2%) and increased over the three trimesters. Pregnant women with a history of economic difficulties, poor marital relationships, common mental disorders, poor social support, bad obstetric history, and exposure to violence were more likely to report antenatal depression. The risk of having preterm birth (2.41; 1.47-3.56) and low birth weight (1.66; 1.06-2.61) was higher in depressed mothers compared to mothers without depression. Conclusions Antenatal depression was higher in low-income countries than in middle-income countries and was found to be a risk factor for low birth weight and preterm births. The economic, maternal, and psychosocial risk factors were responsible for the occurrence of antenatal depression. While there could be competing priority agenda to juggle for health policymakers in low-income countries, interventions for antenatal depression should be reprioritized as vitally important in order to prevent the poor maternal and perinatal outcomes identified in this review.