Most livelihood research focuses on micro-level decisions affecting occupations but fails to examine wider scale processes that shape markets, institutions, and thus livelihood choices. A political ecology framework can help address this gap by providing ways to analyse how multi-scalar and extra-local practices, policies, and discourses affect local-level socio-environmental outcomes. In the qualitative research reported here, that framework is applied to Tha Kam, a peri-urban coastal sub-district of Bangkok, where most residents are small-scale aquaculture farmers. These farmers have experienced precipitous drops in incomes because of two major environmental changes: coastal erosion and wastewater intrusion. The causes are multiple and complex, and many originate not from practices within Tha Kham but from challenges present at a larger scale or that start upstream. The political and economic drivers of these problems stem from Thailand’s fragmented vertical and horizontal governance structure, unequal class relations in which smallholder farmers and peri-urban residents are marginalised, and lack of accountability and representation. This combination of multi-scalar factors and power imbalances has contributed to evolving injustices of peri-urbanisation, all of which are profoundly geographical in their significance.