Streams play an important role in the global carbon cycle, in part by emitting carbon gases (CO2 and CH4) to the atmosphere. Though we know that substantial amounts of carbon gases emitted from streams are derived from groundwater, we understand less about the spatial variability of groundwater carbon delivery to streams. Thus, our objective was to investigate the spatial patterns of groundwater carbon gas concentrations discharged to streams by linking spatially extensive surveys of groundwater discharge with measurements of groundwater discharge carbon gas concentrations. We used handheld thermal infrared imagery to conduct surveys of groundwater discharging directly into streams from exposed streambanks, based on the thermal contrast between groundwater and surface water. Groundwater discharge samples were collected (393 individual samples collected from 313 locations between 2019 and 2021) across >60 km of stream length surveyed throughout the Farmington River watershed in Connecticut and Massachusetts, USA. We found that CO2 and CH4 concentrations in groundwater discharging to streams are spatially heterogenous, varying by 1.9 and 4.6 orders of magnitude, respectively, across the stream network. We linked sampling locations to modelled locations of groundwater discharge and used existing groundwater flow path models to link our sampling location with contributing groundwater characteristics and land cover at the location of groundwater infiltration. Best fit linear mixed effects models for CO2 and CH4 explained 31% and 49% of variation, respectively, and included groundwater discharge chemistry (dissolved organic carbon, dissolved oxygen, and nitrate), percent riparian forest land cover, percent infiltrating land cover (forest for CO2 and wetland for CH4), and modelled groundwater flow path characteristics (residence time for CO2 and groundwater discharge rate for CH4). This study highlights the spatial variability of groundwater carbon gas concentrations in a mixed land-use watershed, and underscores the importance of understanding the multi-scale spatial controls on groundwater discharge carbon gas dynamics.