A new nickel tellurite oxohalide, Ni₁₅Te₁₂O₃₄Cl₁₀, has been prepared by chemical vapour transport reactions and the crystal structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P with the pseudomonoclinic cell parameters a = 10.3248(6) Å, b = 10.3249(6) Å, c = 11.6460(8) Å, α = 73.782(6)°, β = 73.782(6)°, γ = 63.51(2)°, Z = 1, R₁ = 0.0264. The Ni²⁺ ions have octahedral [NiO₆] and [NiO₄Cl₂] coordinations, the Te⁴⁺ ions have one-sided [TeO₃] and [TeO₄] coordinations. The crystal structure can be described as consisting of nickel oxide ribbons extending along (001) that are connected by corner sharing [TeO₃] and [TeO₄] groups to build the open framework structure. The chlorine atoms and the Te-lone pairs are facing voids in the oxide framework. The new compound undergoes two successive antiferromagnetic ordering transitions at 50 K and 10 K. The Curie–Weiss temperature obtained from detailed evaluation of the high-temperature magnetic susceptibilities is positive indicating predominant ferromagnetic superexchange interactions between the Ni magnetic moments.