Efficient heat transfer from the downhole environment to the surface is a key function of drilling fluids, essential for cooling drill bits and maintaining tool reliability. Enhancing the thermal conductivity of drilling fluids is an effective strategy to improve heat dissipation and support deep oil and gas development. Nanomaterials, owing to their nanoscale dimensions, large specific surface area, and high intrinsic thermal conductivity, have shown strong potential for improving drilling fluid thermal management. Recent studies demonstrate that incorporating nanomaterials can significantly increase drilling fluid thermal conductivity and enhance wellbore cooling efficiency during circulation. This review provides a systematic summary of advances in nanomaterial-enhanced drilling fluid heat-transfer performance, covering: (1) heat-transfer mechanisms during drilling; (2) high-temperature impacts on drilling fluid properties, wellbore stability, and tool reliability; (3) thermal-conductivity characteristics of nanomaterials and governing factors; (4) reported enhancement using diverse nanomaterials; and (5) underlying heat-transfer mechanisms. Findings indicate that one-dimensional (e.g., carbon nanotubes) and two-dimensional nanomaterials (e.g., graphene) are more effective in improving thermal conductivity than zero-dimensional nanomaterials. Moreover, enhancing thermal conductivity is generally more effective in water-based drilling fluids due to easier nanoparticle dispersion and lower interfacial thermal resistance, whereas oil-based fluids require extensive surface modification of nanomaterials and usually achieve comparatively smaller improvements. Critical challenges include improving nanomaterial dispersibility and stability under harsh conditions, balancing thermal-transfer enhancement with rheological and filtration performance, and addressing economic and environmental considerations. Future research should focus on hybrid-structure design, integration of low-dimensional nanomaterials, development of responsive intelligent additives, and exploration of sustainable bio-based options.