We systematically investigate the solidification microstructure and elemental segregation in Inconel 738LC fabricated via laser-based powder bed fusion of metals (PBF-LB/M) under three representative process conditions. Microstructural characterizations confirm a strong correlation between thermal input, solidification behavior, and microstructural anisotropy. Within the conditions, the high laser power and scan speed result in low porosity, low micro-cracks, and minimum lack-of-fusion defects. A combination of three-dimensional finite element method (FEM) simulations and phase-field modeling (PFM) quantify the thermal gradients, cooling rates, and predicts dendritic growth behavior. Optimized laser power and scan speed lead to a relatively low thermal gradient, which gives dendrite impingement. The dendrite impingement decreases undercooling, thereby lowering solute partitioning ratio between cell core and cell boundary. The high laser power condition induces a relatively low interface velocity with a larger tip radius, lowering solute segregation of γ’ forming elements based on the Gibbs-Thomson effect. Thus, the high laser power condition gives a relatively low volume fraction of MC carbides, possibly enhancing γ’ precipitation for strength during the post heat treatment process. This work provides new insights into the process-structure–property relationship in PBF-LB/M of IN738LC and establishes a modeling framework for predicting microstructure and segregation phenomena in Ni-based superalloy.