The thermal reactions of Cu with CuBr and Bi₂S₃ yielded black, shiny needles of the mixed-valent compound Cu₃Bi ₂S₃Br₂ = (Cu^I)₆(Bi ^II₂)(Bi^III)₂S₆Br ₄. This first low-valent copper bismuth chalcogenide halide crystallizes in the orthorhombic space group Pbam with a = 2966.9(7) pm, b = 802.4(2) pm, and c = 389.1(3) pm at 293(2) K. The crystal structure is dominated by ${2}\atop{\infty}$[Bi₄S₆Br ₄]^6- layers parallel to (100). The copper(I) cations fill trigonal or tetrahedral voids in the packing of anions. The bismuth(III) cations are in monocapped trigonal prismatic coordination. The bismuth(II) cations form Bi₂⁴⁺ dumbbells (Bi-Bi 306.3(3) pm) that are pairwise combined in cyclic fragments [(Bi^II₂)₂S ₄Br₄]^4-. The structural information on the ordering of the dumbbells is not properly transferred between neighboring layers, resulting in diffuse X-ray scattering along a*. Raman spectroscopy shows a resonance at 113 cm^-1, which can be attributed to the vibration of the Bi₂⁴⁺ unit.