A new ternary aluminide, La₂NiAl₇, has been synthesized from the elements in sealed silica tubes. The crystal structure of La₂NiAl₇ was determined by single-crystal X-ray diffraction and crystallizes in the tetragonal space group I4mm (No. 123) with Z = 4 and lattice parameters a = 6.221(3) and c = 21.403(2) Å. Refinement based on F₀² yielded R₁ = 0.0313 and wR₂ = 0.0392 [I > 2σ(I)]. It is a new structure type, which belongs to the family of BaAl₄-related structures. The La₂NiAl₇ structure corresponds to a 3D superstructure (√2a × √2b × 2c) of the BaAl₄-structure type, whereas La₃Al₁₁ is only a 1D superstructure (3a × b × c). Tight-binding band structure calculations using the density functional theory have been carried out to understand the structural stability of La₂NiAl₇ as well as La₃Al₁₁.