The extent to which tumour-infiltrated brain tissue contributes to cognitive function remains unclear. While prior studies have suggested involvement of tumour-infiltrated tissue in local circuits associated with language and motor function, it is unknown whether such tissue participates in distributed networks important for higher-order cognitive abilities like executive function. In this study, we tested the hypothesis that cortical tissue infiltrated by diffuse low-grade gliomas participates in large-scale cognitive circuits using a unique combination of intracranial electrocorticography (ECoG) and resting-state functional magnetic resonance (fMRI) imaging in four patients. We observed significant task-related high gamma (70-250 Hz) power modulations in tumour-infiltrated cortex in response to increased cognitive effort, implying preserved functionality of neoplastic tissue for complex tasks. Strikingly, we found that tumour locations corresponding to task-responsive electrodes exhibited functional connectivity patterns that significantly co-localised with canonical brain networks implicated in executive function. Finally, we discovered that tumour regions with larger task-related high gamma power elevations tended to be more functionally connected to the dorsal attention network, further demonstrating the participation of tumour-infiltrated cortex in large-scale brain networks that support executive function in health. Overall, this study contributes convergent fMRI-ECoG evidence that tumour-infiltrated cortex participates in large-scale neurocognitive circuits, reflecting preserved functionality of neoplastic brain tissue relevant to clinical management.