Due to the rapidly degradative mechanical performance of selective laser melted (SLM) Al–12Si at elevated temperatures, an Al–12Si–Ti alloy was synthesized by SLM processing with a powder mixture consisting of Al–12Si and 1 wt% of Ti nanoparticles to improve its thermal stability at mid-temperatures (573 K). The results demonstrate that the addition of Ti nanoparticles (i) enlarges the parameter window of SLM processing (power inputs of 200–350 W and scanning speeds of 600–1600 mm/s), (ii) stimulates a columnar to equiaxed transition and refinement of grains (average grain size decreases from 9.0 μm to 1.5 μm), (iii) forms Al3Ti phase improving the thermal stability of Al–Si eutectic cell structure, and (iv) partially suppresses the precipitation of Si phase and coarsening of cell structure at elevated temperatures. These features lead to an improved yield strength of SLM Al–12Si–Ti compared with SLM Al–12Si. Specifically, SLM Al–12Si–Ti annealed at 573 K possesses a higher yield strength (297 ± 10 MPa) than SLM Al–12Si (207 ± 9 MPa) annealed at the same conditions. This study will pave the way for the design and synthesis of SLM Al alloys with improved structural and mechanical stability by minor alloying via nanoparticle addition.