The first ITER toroidal field coil (TFC) has been successfully manufactured by the Japanese Domestic Agency in January 2020. The ITER TFCs are the largest Niobium Tin (Nb3Sn) superconducting magnets in the world; each is enclosed in an austenitic stainless-steel case with a height of 16.5 m and total weight is 310 tons (Knaster et al 2008 IEEE Trans. Appl. Supercond.18 495–498). A set of 18 TFCs will be installed around vacuum vessel to function as a plasma confinement magnet system. The responsibility to procure 18 TFCs and 1 spare coil is shared between European Domestic Agency and Japanese Domestic Agency (Bellesia et al 2020 IEEE Trans. Appl. Supercond.30 4202205; Sborchia et al 2008 IEEE Trans. Appl. Supercond.18 463–466). To hold a common magnetic and geometrical properties among all the TFCs, tight tolerances of sub-millimeter order are defined on each TFC. The fabrication of those massive magnets with such tight tolerances involved some major technical challenges. These technical challenges were solved by pre-assessment and process qualification through some qualification trials. As a result, techniques established to solve those challenges were implemented to the TFC manufacturing, leading to the successful completion of the first TFC. The details are described in the paper.