This study systematically maps, assesses and aggregates research relating to postnatal depression (PND) and poverty in low and lower middle income countries (LLMICs). Our search of 12 databases yielded 2,202 articles, of which 47 items from 17 countries were included in our mapping. We highlight mechanisms for the relationships between poverty and PND in LLMICs. The research base on the relationships between poverty and PND in LLMIC is limited, but has recently expanded. It is dominated by studies that consider whether poverty is a risk factor for PND. Income, socio-economic status and education are all inconsistent risk factors for PND. Clues to better ways of framing and capturing economic stress in PND research is found in the qualitative studies included in our mapping. Evidence focuses overwhelmingly on individual-level analyses. To understand the scale and implications of PND in LLMICs, research has to take account of neighbourhoods, communities, and localities.