We present a single-shot, high-temporal-resolution terahertz diagnostic capable of measuring free-space far-infrared electromagnetic fields in time and space. We show that by using a chirped probe electro-optic sampling technique, in combination with a recently described interferometric retrieval algorithm [Appl. Phys. Lett. 87, 211109 (2005)], the diagnostic can provide transform-limited temporal resolution, mainly limited by the spectral bandwidth of the optical probe pulse, regardless of its chirp.