Abstract Floodplains are important organic carbon (OC) storage sites, and the evolution of watercourses modulates the transport, burial and reworking of organics with cascading effects on watershed CO 2 budgets. Meandering rivers have broadly predictable patterns of channel-planform evolution, providing an opportunity to assess floodplain OC budgets of relation to characteristic migration paces and floodplain ages. However, due to geomorphic complexities of individual meandering rivers, assessments of relationships between channel and OC dynamics have thus far remained limited. We illustrate evolving OC budgets in relation to channel migration in the Vermilion River (Ontario) located in the boreal forest of eastern North America. We combine photogrammetric analyses and dynamic time warping of channel centrelines with analysis of top-soil bulk density and OC. We found that variations of OC stock per unit surface area and soil development are modulated by meander migration through the development of typical boreal-forest vegetation successions. Our results support the hypothesis that meander migration controls soil development, forest age and floodplain OC budgets. We anticipate our study to inform wider applications to rivers in different bioclimates – an approach that may in turn help carbon assessment in the context of changing climate or land use.