The three peridotite massifs in the Zabargad island (northern Red Sea) document the exhumation of the mantle during continental rifting and the rift to drift transition. Deformation evolved from pervasive at the massif scale to localized in metric shear zones. To characterize the active processes and the role of melts and aqueous fluids in the deformation, we performed a petrostructural study of 40 samples representative of the different stages of deformation in the three massifs. Microstructures recording synkinematic crystallization of plagioclase, clinopyroxene, and orthopyroxene in the southern and amphibole-bearing spinel-websterite layers in the central and northern massifs indicate that pervasive deformation occurred in the presence of melts, but at lower pressure in the south. In the shear zones, deformation was accommodated by concomitant dislocation and dissolution-precipitation creep. Evolution from protomylonites to ultramylonites produced increasing volumes of a fine-grained polymineralic matrix where amphibole progressively replaces plagioclase and clinopyroxene. Fluid-assisted deformation at all stages is attested by the interstitial shapes of pyroxene neoblasts intermixed with olivine in the matrix. Local deformation at the brittle-ductile transition is accompanied by the crystallization of scapolite. Thermobarometry and thermodynamic modelling constrained by the microstructural observations document shearing under decreasing pressure and temperature from near solidus conditions at >1 GPa in the north and central massifs and ~0.7 GPa in the southern massif to < 600°C and <0.3 GPa in all three massifs. These data also imply increasing hydration, indicating fluid focusing and local aqueous fluid saturation in the shear zones, with sea water ingression to >10 km depth. However, fluid supply was spatially heterogeneous and probably intermittent, with equilibrium only achieved locally in the ultramylonites. The present study documents therefore how progressive strain localization and fluid-focusing in extensional shear zones enable thinning and exhumation of the mantle during continental rift and rift-to-drift transition.