Large-scale electrical resistivity investigations of the Antarctic crust and upper mantle utilizing the magnetotelluric method (MT) are limited in number compared to temperate regions, but provide physical insights difficult to obtain with other techniques. Key to the method’s success in polar environments are instrumentation advances that allow micro-volt level measurements of the MT electric field in the face of mega-ohm contact resistances. In this presentation, we analyze MT data from four campaigns over the Antarctic interior using modern 3D non-linear inversion analysis and offer additional geophysical conclusions and context beyond the original studies. A profile of MT soundings over transitional Ellsworth-Whitmore block in central West Antarctica implies near-cratonic lithospheric geothermal conditions with interpreted graphite-sulphide horizons deformed along margins of high-grade silicate lithologic blocks. Data across South Pole soundings confirms large-scale low resistivity spanning Moho depths that is consistent with limited seismic tomography and elevated crustal thermal regime inferences. Upper mantle under a presumed adiabatic thermal gradient below the Ross Ice Shelf region of West Antarctica appears to be of a moderately hydrated state but not sufficient so as to induce melting. The degree of hydration there is comparable to that below the north-central Great Basin extensional province of the western U.S. Comprehensive 3D coverage of Mount Erebus and Ross Island reveals unprecedented views of the magmatic plumbing feeding the phonolitic volcanic system. This includes a lower middle crustal staging area for episodic magmatic replenishment of the upper middle crustal chamber hosting phonolitic differentiation, which in turn is fed from an upper mantle source region of the parental basanite.