This study investigates the effect of titanium diboride (TiB2) nanoparticles on the properties of nickel superalloy VZh159 fabricated by selective laser melting (SLM). The study examines the density and microhardness of composites containing 0 to 2 wt.% TiB2 under various SLM processing modes with energy densities ranging from 49.8 to 169.3 J/mm3. Density measurements were conducted using hydrostatic weighing, achieving samples with density exceeding 99% of the theoretical value at optimal process parameters. The study reveals that increasing TiB2 content shifts the optimal energy density toward higher values: for pure VZh159 it is 83.3–86.8 J/mm3 and for composites with 1.5% and 2% TiB2 it exceeds 130 J/mm3. The research demonstrates progressive microhardness enhancement with increasing TiB2 concentration, from 280–290 HV for the pure alloy to 320–348 HV for 2% TiB2 composite. The study determines the optimal TiB2 content as 1–1.5 wt.% at energy density of 110–140 J/mm3, providing 15–20% microhardness improvement.