Breastfeeding is associated with many health benefits, while its prevalence is determined by numerous factors, including socioeconomic status (SES). SES is the position of an individual on the socioeconomic scale, using occupation, education, income, place of residence, and wealth as key indicators. Since its interrelationship with health is complex, world region-specific insights into the relevant socioeconomic inequalities impacting breastfeeding practices are crucial to effectively address these. The purpose of this systematic review is, therefore, to explore SES indicators affecting breastfeeding initiation and duration in two different United Nations-defined regions, Western Europe and Southern Africa to assess (dis)similarities, as these can guide region-specific, targeted interventions to improve practices. A systematic literature search was conducted across seven databases, of which 47 articles were included. The risk of bias was assessed, and outcome data related to SES as well as breastfeeding initiation and duration were collected. Higher education consistently leads to better breastfeeding initiation outcomes, but economic constraints and employment in informal sectors hinder breastfeeding practices in Southern Africa. In Western Europe, supportive working conditions and a migration background have a positive impact, while employment status and income show rather mixed effects. Community, regional, and religious factors play significant, ambiguous roles. In South Africa, food insecurity, the living environment, and geographic location complicate breastfeeding. This systematic review highlights the significant influence of SES on breastfeeding initiation and duration in Western Europe and Southern Africa, while the specific factors indeed vary between both regions. This systematic review therefore illustrates the relevance of region-specific SES factors, impacting breastfeeding practices. Addressing these barriers with region-specific, targeted approaches may result in substantial progress toward achieving global breastfeeding goals. Registration: PROSPERO (CRD42023473433).