High-entropy alloys (HEAs) offer exceptional mechanical properties due to their unique solid solution structures. However, conventional face-centered cubic  single-phase HEAs exhibit limited strength. While introducing L1₂ precipitates can simultaneously improve strength and plasticity, conventional casting methods cannot effectively produce large, complex components. Laser powder bed fusion (L-PBF) technology has emerged as a solution for fabricating complex geometrically intricate HEA parts. However, the extremely high cooling rates associated with this technology present a dual challenge: suppressing the precipitation of strengthening phases and generating significant residual stresses, which negatively affect the material’s high-temperature performance. Current research in additive manufacturing of HEAs primarily focuses on optimizing performance at room temperature and intermediate temperatures (≤ 800 °C). Studies exploring non-equilibrium microstructural evolution and mechanical behavior under ultra-high temperatures (≥ 900 °C) are lacking, thus failing to address the urgent need for extreme heat-resistant materials in fields such as aerospace and nuclear energy. In this study, a precipitation-strengthened NiCoCr-based HEA was fabricated using L-PBF technology, and a systematic investigation was conducted into how different heat treatment processes (including aging treatment and solution treatment immediately followed by aging treatment) affect its microstructure and mechanical properties. The results show that optimized L-PBF parameters (laser power of 200 W and scanning speed of 1000 mm/s) enable the production of defect-free samples with a density of 99.64%, characterized by columnar crystals and dendritic segregation in the as-fabricated state. After undergoing solution and aging treatment, the sample exhibited a 21.4% increase in room temperature yield strength ((732 ± 7) MPa) and a 24.3% enhancement in tensile strength ((1075 ± 13) MPa) compared to the as-fabricated sample. This was attributed to recrystallization and modulation of the precipitation phases (L1₂ and σ phases). Notably, the elongation after fracture remained at (18 ± 4)%. By contrast, aging the samples alone resulted in significant loss of plasticity (only (3 ± 1)% elongation) due to extensive grain boundary precipitation of the σ phase and high residual stresses. During high-temperature (900 °C) tensile testing, the solution and aging-treated sample demonstrated the highest tensile strength of (273 ± 15) MPa and an elongation of (13 ± 2)%. Microstructural analysis indicated that the solution and aging treatments effectively balanced the strength–ductility synergy by promoting recrystallization, modulating the properties of the precipitates (such as distribution and quantity etc.), and introducing annealing twins.