Background: In South Africa almost 2 million women work informally. Informal work is characterised by poor job security, low earnings, and unsafe working conditions, with high rates of poverty and food insecurity. The peripartum period is a vulnerable time for many working women. This study explored how mothers navigate the tension between the need to work and needing to take care of a newborn baby, and how this affects their feeding plans and practices. Methods: A mixed methods longitudinal cohort method was employed. Informal workers were recruited in the last trimester of pregnancy during an antenatal visit at two clinics in Durban, South Africa. Data were collected using in-depth interviews and quantitative questionnaires at three time points: pre-delivery, post-delivery and after returning to work. Framework analysis was used to analyse qualitative data in NVIVO v12.4. Quantitative analysis used SPSSv26. Results: Twenty-four participants were enrolled and followed-up for a period of up to one year. Informal occupations included domestic work, home-based work, informal trading, and hairdressing, and most women earned <R3000 (US$175) per month. Participants had good knowledge of the importance of breastfeeding for child health. Most women planned to take time off work after the birth of their babies, supporting themselves during this time with the child support grant (CSG) received for older children, their savings, and support from the baby’s father and other family members. However, financial pressures forced many mothers to return to work earlier than planned, resulting in changes to infant feeding practices. Several mothers tried expressing breastmilk, but only one was able to sustain this while away from the baby. Most participants introduced formula, other foods and fluids to their babies when they returned to work or stopped breastfeeding entirely, but some were able to change their work or adapt their working hours to accommodate breastfeeding. Conclusions: Interventions are needed within the social and work environment to support mothers with breastfeeding while they continue earning an income in the informal economy. The extension of the CSG to the antenatal period could assist mothers to stay at home longer post-delivery to breastfeed their babies.