This study examines pore morphology, size characteristics, and spatial arrangement in laser beam powder bed fusion (LB-PBF) 316L stainless steel cylindrical preforms subsequently machined into tensile samples. The preforms were fabricated in vertical, horizontal, and 45° build orientations and analysed in the as-printed condition and after annealing, followed by water quenching. Quantitative pore characterisation was performed using SEM-based ImageJ analysis, with descriptors including pore size, shape, and spatial distribution. These data were examined alongside tensile properties and melt-pool-scale microstructural observations. The results show orientation-dependent differences between the as-printed and heat-treated post-mortem pore populations. The most pronounced changes were observed for the 45° and vertical conditions, where pore count increased from 7.25 to 150.38 and from 10.60 to 325.21 pores per analysed field, respectively, while mean pore area decreased from 0.532 to 0.075 µm² and from 0.769 to 0.108 µm². In all orientations, annealing reduced 0.2% proof strength and ultimate tensile strength while increasing elongation; elongation increased from 37.8% to 49.7% for the 45° condition, from 31.8% to 39.6% for the horizontal condition, and from 42.4% to 55.3% for the vertical condition. The strength reduction is consistent with heat-treatment-induced modification of the LB-PBF microstructural state, while mechanisms such as recovery and residual-stress relief may have contributed to the observed response. The heat-treated conditions also exhibited smaller and more regular detected pore features, which may have contributed to the increased ductility. The study demonstrates that morphology-resolved pore analysis provides a more informative basis for interpreting defect-sensitive mechanical behaviour in LB-PBF 316L than conventional porosity metrics alone.