A pure organic single crystal, [H(2)dabco]center dot[2CB](2) ([H(2)dabco](2+) = diprotonated 1,4-diazabicyclo[2.2.2]octane, 2CB(-) = 2-chlorobenzoate), which undergoes a ferroelectric-to-paraelectric phase transition above room temperature (similar to 323 K upon heating), was prepared and characterized. This ferroelectric crystal possesses a distinctive supramolecular architecture composed of discrete H-bonded trimeric units (two 2CB(-) anions bridged by one [H(2)dabco](2+) cation through N-H center dot center dot center dot O hydrogen bond interactions). In the paraelectric phase, the [H(2)dabco](2+) cation is rotationally disordered and lies at the symmetric center of the trimer. Upon cooling, it is frozen in an ordered state and deviates toward a 2CB(-) anion at one end along the H-bond. The collective displacement of the cations leads to a polarization of the single crystal along the crystallographic c axis, which is confirmed by the temperature dependence of the second harmonic generation and spontaneous polarization. A significant increase in the phase transition temperature of the deuterated analogue suggests that the proton plays an important role in the ferroelectric phase transition.