The discovery of the thioformyl radical (HCS) was reported in 2018 by Agúndez and co-workers toward L483, a dark cloud with an embedded Class 0 protostar. The observations were made with the IRAM 30m telescope. The detection was based on rotational data measured and analyzed by Habara et al. One possible formation pathway to HCS is the reaction between C atoms and hydrogen sulfide (H₂S), which has been shown to be efficient by both experimental and theoretical studies.

HCS is a radical of thioformaldehyde (H₂CS), which was detected in 1973. The HCS⁺ cation has also been detected. The isomer HSC was also detected toward L483. These species are sulfur-containing versions of detected oxygen-bearing compounds: formaldehyde (H₂CO), formyl radial (HCO), and its cation, (HCO⁺).