Low-temperature atomic layer deposition (ALD) is increasingly important for the integration of layered metal dichalcogenides such as tin diselenide (SnSe₂) into advanced nanoelectronic devices, where compatibility with temperature-sensitive substrates and precise thickness control are essential. Using a novel and highly reactive selenium precursor, namely, bis(trimethylstannyl)selenide or Se(SnMe₃)₂, SnSe₂ films are deposited at reduced temperatures. As-deposited films are initially amorphous, however, post-deposition annealing at 250°C induces crystallization. Structural analysis reveals a clear evolution in crystallinity: ultrathin films (∼25 nm) exhibit nearly single-crystalline, defect-free domains, while thicker films (∼100 nm) transition to a polycrystalline structure. This controlled variation in crystal quality directly influences the electronic transport properties, demonstrating the potential of low-temperature ALD combined with mild annealing for scalable fabrication of high-performance, thickness-engineered SnSe₂-based devices.