Abstract: The application of 1000 MPa-grade high-strength steel in the hydropower sector has become increasingly mature. However, the domestic development of corresponding high-performance welding consumables remains limited. One of the key challenges in the research and development is maintaining high toughness at low temperatures in high-strength deposited metal. In this study, the deposited metal of 1000 MPa-grade high-strength steel submerged arc welding was optimized by adding Ce elements. Microstructural characterization methods, including SEM, TEM, and CLSM, were employed to investigate the effects of Ce content on the strength-toughness properties and microstructural evolution of the deposited metal. The results indicate that when the Ce content is 0.02%, the tensile and yield strengths are increased by 3.7% and 17.2%, respectively, achieving the best balance between strength and toughness. The low-temperature impact toughness is generally enhanced, with the most significant improvement observed at a Ce content of 0.01%, showing increases of 24.3% and 42.2% at −40 ℃ and −60 ℃, respectively. Microstructurally, Ce can refine grains, resulting in a more dispersed distribution of M-A constituents and enhancing the toughness of the microstructure. However, when the Ce content reaches 0.04%, the sizes of blocky ferrite and acicular ferrite increase, along with a higher proportion of large grains, adversely affecting the tensile strength. In terms of the evolution mechanism, the synergistic enrichment of Ce and C induces lattice distortion, promoting the formation of M-A constituents. At a Ce content of 0.02%, the residual austenite content increases, leveraging the TRIP effect to enhance plastic deformation capacity and facilitating the transformation of lower bainite, thereby achieving a synergistic improvement in strength and toughness. In contrast, a Ce content of 0.04% leads to exacerbated grain boundary segregation, the formation of Ce-containing brittle phase precipitates, and reduced austenite stability, resulting in a deterioration of impact toughness compared to that at a Ce content of 0.02%.