In this work, we report a novel iridium(III)-based luminescent switch on-off-on probe, for the in vitro and in vivo detection of sulfide ion. The mechanism of this platform is based on the effective charge transfer quenching of the iridium(III) complex 1 by Fe3+, followed by the restoration of luminescence upon the addition of Na2S. The probe, hereinafter referred to as 1 Fe3+, exhibited a linear range of detection for Na2S from 0.01 to 1.5 mM, with a detection limit of 2.9 1.1M at signal-to-noise ratio (S/N) of 3. We also demonstrate the utility of 1 Fe3+ for cell-based imaging as well as for the detection of enzymatic sulfide generation in living zebrafish.