The world's first Nuclear Magnetic Resonance (NMR) system with an operating frequency above 1 GHz was developed and operated at the National Institute for Materials Science (NIMS) during 2014–2015. The Nb₃Sn innermost coil of an existing 920 MHz (21.6 T) NMR magnet was replaced with a Bi-2223 layer-wound coil, upgrading the magnet to 1.03 GHz (24.2 T). At 1.02 GHz (24.0 T), shimming started to achieve the homogeneous magnetic field required for NMR measurements. However, large magnetic-field inhomogeneity appeared that was capable of being compensated using the superconducting (SC) and room temperature (RT) shim coils installed. We used a powerful and fast-acting shimming method that combines ferromagnetic shim, SC shim and RT shim to compensate the inhomogeneity. This achieved effective compensation of the magnetic-field inhomogeneity, subsequently leading to an excellent NMR resolution test result of 0.7 ppb (0.7 × 10^-9). This NMR resolution will enable NMR measurement of a membrane protein sample.