C

\nContext. A powerful tool with which to probe the gas content at high redshift is the [C <sc>II</sc>] 158 μm submillimetre emission line, which, due to its low excitation potential and luminous emission, is considered a possible direct tracer of star forming gas.\nAims. In this work, we investigate the origin, evolution, and environmental dependencies of the [C <sc>II</sc>] 158 μm emission line, as well as its expected correlation with the stellar mass and star formation activity of the high-redshift galaxies observed by JWST.\nMethods. We use a set of state-of-the-art cold-gas hydrodynamic simulations (C<sc>OLD</sc>SIM) with fully coupled time-dependent atomic and molecular non-equilibrium chemistry and self-consistent [C <sc>II</sc>] emission from metal-enriched gas. We accurately track the evolution of H <sc>I</sc>, H <sc>II</sc>, and H2 in a cosmological context and predict both global and galaxy-based [C <sc>II</sc>] properties.\nResults. For the first time, we predict the cosmic mass density evolution of [C <sc>II</sc>] and find that it is in good agreement with new measurements at redshift z = 6 from high-resolution optical quasar spectroscopy. We find a correlation between [C <sc>II</sc>] luminosity, L[C <sc>II</sc>], and stellar mass, which is consistent with results from ALMA high-redshift large programs. We predict a redshift evolution in the relation between L[C <sc>II</sc>] and the star formation rate (SFR), and provide a fit to relate L[C <sc>II</sc>] to SFR, which can be adopted as a more accurate alternative to the currently used linear relation.\nConclusions. Our findings provide physical grounds on which to interpret high-redshift detections in contemporary and future observations, such as the ones performed by ALMA and JWST, and to advance our knowledge of structure formation at early times.\n