Abstract: Two heats of M2 high-speed steel with different rare-earth (Ce) contents were produced by a domestic steel plant using the following process route: electric arc furnace (EAF) smelting → ladle furnace (LF) refining → vacuum degassing (VD) → electroslag remelting (ESR) → forging → rolling. Optical microscopy, scanning electron microscopy, X-ray diffraction analysis, and high-temperature confocal microscopy were used to investigate the effects of Ce on the inclusions and carbides in M2 high-speed steel. The results indicated that the addition of Ce reduced the oxygen and sulfur contents in the electroslag ingot. The inclusions were completely modified, with large irregular Al₂O₃ inclusions becoming small globular CeAlO₃ inclusions. Meanwhile, their number density and average size decreased. Although the number density only decreased by 12%, from 450 to 396, the average size decreased by 43.1%, from 1.81 to 1.03 μm. The cleanliness of the molten steel was significantly improved. Thermodynamic calculations indicated that CeAlO₃ inclusions had the lowest Gibbs free energy and were therefore the most likely to form in the electroslag ingot. The eutectic carbides found in the as-cast structure of an electroslag ingot with the Ce addition exhibited a finer size, smaller quantity, and partial fragmentation of the network structure. A high-temperature confocal laser scanning microscope was used for in-situ observations of the solidification processes of the two groups of test steels, and the degree of mismatch was calculated. The results showed that the degree of mismatch between (001) CeAlO₃ and (100) γ-Fe was 4.49%, indicating that CeAlO₃ inclusions could serve as effective heterogeneous nucleation cores for γ-Fe. This promoted an increase in nucleation sites during the solidification of molten steel, which greatly compressed the growth space of eutectic carbides, and thereby inhibited the precipitation of eutectic carbides. This was consistent with the observation results from the high-temperature confocal microscopy. In both groups of annealed wire rods, the carbides were M₆C, MC, and M₇C₃. The addition of Ce did not change the type of carbides in the wire rod. The microstructure of the annealed wire rod consisted of coarse primary carbides and smaller spheroidized pearlitic carbides. The addition of Ce decreased the amount of large carbides while increasing the proportion of fine pearlitic carbides. The statistical results for the carbides in a longitudinal section of the wire rod showed that after the addition of Ce, the number of carbides increased from 733 to 1145 in the same area (1000 μm²), representing a 56.21% increase. Meanwhile, the area fraction of carbides decreased from 12.87% to 8.06%, a reduction of 37.37%. The influence of Ce on the inclusions and carbides improved the properties of the M2 high-speed steel. The research results provide theoretical support for the production of high-quality M2 high-speed steel.