The formation of the transparent conductive oxide SnO₂:Ta by reactive direct-current magnetron sputtering at a low temperature of 225°C was studied as a function of the oxygen flow rate using a pilot-scale setup. Beginning with a mixture of β-Sn and SnO as majority phases and minority fractions of Sn₃O₄ and SnO₂ at very low O₂ flows, up to the formation of phase-pure rutile-type SnO₂:Ta at higher flow rates, a systematic evolution of the phase structure is observed. The SnO₂:Ta (0.70 at.% Ta) film grown at optimized flow conditions exhibits a transmittance of >80% from 500 to 2500 nm and a specific resistivity of 0.3 Ω cm. While the transmittance is competitive, the resistivity is in the upper range of that reported for low-temperature-deposited SnO₂:Ta films in research lab studies. Based on X-ray diffraction, Raman spectroscopy, optical spectroscopy, and X-ray photoelectron spectroscopy, we conclude that the small crystallite size, microstrain, and point defects caused by the low growth temperature might prevent charge carrier activation, even though the Ta dopant is incorporated as Ta⁵⁺ in the rutile-type SnO₂ lattice.