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Northern peatlands are a globally significant source of methane (CH4), and emissions are projected to increase due to warming and permafrost loss. Understanding the microbial mechanisms behind patterns in CH4production in peatlands will be key to predicting annual emissions changes, with stable carbon isotopes (δ13C‐CH4) being a powerful tool for characterizing these drivers. Given that δ13C‐CH4is used in top‐down atmospheric inversion models to partition sources, our ability to model CH4production pathways and associated δ13C‐CH4values is critical. We sought to characterize the role of environmental conditions, including hydrologic and vegetation patterns associated with permafrost thaw, on δ13C‐CH4values from high‐latitude peatlands. We measured porewater and emitted CH4stable isotopes, pH, and vegetation composition from five boreal‐Arctic peatlands. Porewater δ13C‐CH4was strongly associated with peatland type, with δ13C enriched values obtained from more minerotrophic fens (−61.2 ± 9.1‰) compared to permafrost‐free bogs (−74.1 ± 9.4‰) and raised permafrost bogs (−81.6 ± 11.5‰). Variation in porewater δ13C‐CH4was best explained by sedge cover, CH4concentration, and the interactive effect of peatland type and pH (r2= 0.50, p< 0.001). Emitted δ13C‐CH4varied greatly but was positively correlated with porewater δ13C‐CH4. We calculated a mixed atmospheric δ13C‐CH4value for northern peatlands of −65.3 ± 7‰ and show that this value is more sensitive to landscape drying than wetting under permafrost thaw scenarios. Our results suggest northern peatland δ13C‐CH4values are likely to shift in the future which has important implications for source partitioning in atmospheric inversion models. Peatlands are abundant across the boreal‐Arctic landscape and are important sources of methane, a powerful greenhouse gas. The amount of methane emitted into the atmosphere depends on multiple factors including the organic material being decomposed and the microbial processes (“pathways”) that produce methane. The different pathways of methane production leave distinct fingerprints (“stable carbon isotopes”) on methane that provide information on how that methane was formed and help to trace methane in the atmosphere back to its ground source. We looked at how stable carbon isotopes change across five northern peatland locations and wanted to know what controls those changes. We found that stable carbon isotopes differ between bogs and fens and are further controlled by soil pH and the abundance of sedge vegetation present. We used this information to test how stable carbon isotopes from northern peatlands might change as the landscape becomes wetter or drier due to the impacts of climate change. We found that peatland stable carbon isotopes are most sensitive to potential landscape drying opposed to wetting which has important implications for improving methane emission models. Porewater δ13C‐CH4values of northern bogs and fens differ from each other and correlate with emitted δ13C‐CH4valuesIn addition to peatland type, vascular plant cover, pH, and CH4concentration help explain variation in porewater δ13C‐CH4valuesThe δ13C‐CH4value for northern peatlands is more sensitive to landscape drying than wetting under permafrost thaw scenarios Porewater δ13C‐CH4values of northern bogs and fens differ from each other and correlate with emitted δ13C‐CH4values In addition to peatland type, vascular plant cover, pH, and CH4concentration help explain variation in porewater δ13C‐CH4values The δ13C‐CH4value for northern peatlands is more sensitive to landscape drying than wetting under permafrost thaw scenarios