New multifold seismic‐reflection and wide‐angle reflection/refraction data across George VI Sound, Antarctic Peninsula, show the presence of graben and horst structures indicating an extensional origin. The data suggest that rocks of an accretionary complex and fore‐arc basin underlie the Sound and are in faulted contact along its eastern boundary with volcanic and plutonic rocks of the associated Mesozoic arc of western Palmer Land. A cover of possible syn‐ and postglacial Cenozoic deposits drapes the structures. The combination of new seismic, synthetic‐aperture radar and previously acquired data suggests subduction‐related rifting in the Sound was segmented, with opening in the south predominately by normal extension whilst in the north, dextral transtension predominated.