•Continuous external Rogowski (CER) diagnostics have been successfully installed and resin encapsulated to ITER's superconducting toroidal field Coils, meeting the desired dimensional accuracy and electrical performance.•Thorough pre-qualification tests had demonstrated the key operations involved in the process of CER integration, and validated the hydraulic and vacuum tightness of the manufactured connection assemblies.•The established integration and resin encapsulation procedure has been validated for high vacuum compatibility and outstanding reproducibility.•Noises are expected to be substantially suppressed for the CER diagnostics integrated to TF Coils, thanks to the low thermonuclear load and favourable service conditions inside superconducting magnets.•As a pioneering attempt of plasma diagnostics integration to reactor-scale superconducting magnets, the success of this venture has significantly implications to the development of cryogenic-based diagnostics for DEMO and future reactors. Continuous External Rogowski (CER) are the primary plasma current diagnostics for the ITER tokamak, as well as the only diagnostics built into the ITER Toroidal Field Coils (TF coils). The integration of CER diagnostics to the TF coils faced numerous technical challenges, such as: the integrated components have to withstand the maximum pressure foreseen during ITER TF coil resin impregnation (350 kPa), comply with the high vacuum requirements that the helium leak rate shall be <2.7 × 10−9 Pa-m3/s, and survive at cryogenic temperature. The CER diagnostics integration campaign turned out to be a marked success, thanks to a comprehensive pre-qualification program and well-coordinated collaborations among the participating parties. All four sets of CER diagnostics have so far been integrated to the respective TF coils. As a pioneering attempt of building plasma diagnostics into reactor-scale superconducting magnets, the potential implications of this venture to the diagnostics development for DEMO and future fusion reactors are discussed. The gained experiences and lessons learned from this venture are summarized at last.