Mn-II(TCNE)[C-4(CN)(8)](1/2) (TCNE = tetracyanoethylene) exhibits a reversible pressure-induced piezomagnetic transition from a low magnetization antiferromagnetic state to a high magnetization ferrimagnetic state above 0.50 +/- 0.15 kbar. In the ferrimagnetic state, the critical temperature, T-c, increases with increasing hydrostatic pressure and is similar to 97 K at 12.6 kbar, the magnetization increases by 3 orders of magnitude (1000-fold), and the material becomes a hard magnet with a significant remnant magnetization.