A high-quality, Cu-doped TiO2 photocatalyst was prepared via a single-step process using an atmospheric-pressure plasma torch system. Degussa P-25 was thermally doped with Cu at Cu/(Cu + TiO2) ratios of 0–5 wt.%. The raw and resulting nanoparticles were characterized using TEM, XRD, UV-Vis, and XPS. TEM showed that the particle size of plasma-treated TiO2 was generally < 50 nm. 67–75% of the resulting particles, by number were between 10 and 20 nm. The remaining particles were < 10 nm (~10%) and between 20 and 30 nm (~10%). The XRD results showed that Cu doping decreased the anatase/rutile crystalline ratio compared to untreated P-25. Nevertheless, the greater the amount of Cu added, the greater the anatase/rutile ratio was for the Cu-doped TiO2. The UV-Vis results showed that the absorption wavelength for plasma-treated TiO2 extended to the visible light range, especially for TiO2 doped with 5 wt.% Cu. The XPS results revealed that the form of Ti was Ti3+ and Ti4+, O was O2–, and Cu was Cu+ and Cu2+. The Hg0 breakthrough tests indicated that the Cu-doped TiO2 underwent appreciable Hg0 removal under visible-light irradiation. Doped Cu effectively suppressed Hg reemission from the TiO2 surface.