Both the nature of the electrical transport and magnetism of high-pressure phases of FeS have been elucidated in relation to the spin-state configuration of Fe. This has been achieved by combined 57FeMössbauer spectroscopy and resistance measurements on samples pressurized in miniature gem-anvil pressure cells to ∼12 GPa in the range 300–5 K. Hexagonal FeS in the range 3–7 GPa exhibits magnetic nonmetallic behavior, whereas monoclinic FeS beyond ∼7 GPa is diamagnetic and nonmetallic. This is compelling experimental evidence to show that, along the room-temperature isotherm, hexagonal FeS has thermally activated charge carriers and a high-spin magnetic-electronic configuration, whereas monoclinic FeS adopts a magnetically quenched low-spin state and concomitant filled valence band.