We present a new probe of primordial non-Gaussianity via the 21-cm radiation from minihaloes at high redshifts. We calculate the fluctuations in the brightness temperature (measured against the cosmic microwave background) of the 21-cm background from minihaloes containing H i at redshift ∼6–20, and find a significant enhancement due to small non-Gaussianity with amplitude fNL ≲ 1. This enhancement can be attributed to the non-linear bias which is strongly increased in the presence of non-Gaussianity. We show that our results are robust against changes in the assumed mass function and some physical aspects of minihalo formation, but are nevertheless sensitive to the presence of strong radiation sources within or around the minihaloes. Our findings are relevant for constraining and searching for small primordial non-Gaussianity with upcoming radio telescopes such as Low-Frequency Array (LOFAR) and Square Kilometre Array (SKA).