The circular economy rationale is increasingly promoted as a means to move from a global plastic waste dilemma to a plastics economy that is aligned with the principles of sustainable development. However, any such effort will have to account for the socio-economic settings in low-income and middle-income countries of the global south which are the main entry points of mismanaged plastic wastes into the environment. Since waste management and recycling in these economies are characterized by a great degree of informality, there is an urgent need to find models for partnering with the informal recycling sector in an effective, scalable, and sustainable manner. In this work, we present the case of a for-profit company located in Nairobi, Kenya, that operates on the interface between formal and informal by processing post-consumer plastics sourced from local waste pickers through a fair-trade-like business model. Economic incentives, trust building measures, and a general willingness to learn and adapt were identified as prerequisites for establishing accountable supplier-buyer relationships. The combination of informed material pre-sorting by the individual waste picker and subsequent industrial scale sorting and washing resulted in recyclates that were comparable to commercially available benchmark recyclates from the sophisticated formal recycling system of a high-income country in terms of both composition and selected engineering properties. High-quality mechanical recycling of plastic wastes under informal conditions seems feasible and may even come along with socio-economic benefits for marginalized waste pickers when suitable modes of cooperation are put in place.