Halide perovskites have continued to rise as attractive light absorber materials, mainly driven by their potential wide applications in the fields of solar cells, photodetectors, lasers and others. However, Pb-containing perovskites are poisonous and could cause serious potential problems to our environment. Thus, there is a strong desire to develop lead-free perovskites as environmentally friendly alternatives. Here, we have shown a successful synthesis of a non-toxic single crystalline double-halide perovskite, Cs3BiBr6, and analysed its structural characteristics in detail. This perovskite represents a new structure in terms of double-halide perovskites. The crystal structure features isolated BiBr6 polyhedra forming a zero-dimensional halide perovskite. The bandgap of this compound is measured to be 2.55 eV. High thermal stability is also clearly shown in the Cs3BiBr6 single crystal. A photodetector based on this compound is fabricated and tested, which exhibits an impressive detectivity of 0.8 × 109 Jones and low dark current under 400 nm light illumination. Overall, our results show that the Cs3BiBr6 perovskite as a lead-free perovskite has interesting structures and promising properties for optoelectronic devices.