Granulites from the Narryer Terrane in the northern Yilgarn Craton, Australia, record evidence for high to ultrahigh thermal gradients during the Meso–Neoarchean. U–Pb zircon ages reflect a complex history of high-grade, prolonged and poly-phase metamorphism, with evidence for several thermal pulses at ca. 2745–2725 Ma, ca. 2690–2665 Ma and ca. 2650–2610 Ma. Forward phase equilibria modelling on rocks with varying bulk compositions and mineral assemblages suggest that peak temperatures reached 880–920 °C at pressures of 5.5–6 kbar at ca. 2690–2665 Ma, followed by near-isobaric cooling. These new pressure–temperature results also indicate that these rocks underwent some of the hottest thermal gradient regimes in the metamorphic record (≥150 °C/kbar). Previous models have inferred that ultrahigh thermal gradients and coeval large-scale anatectic melting in the Narryer Terrane were primarily generated by mantle-driven processes, despite most of the lithological, isotopic and geochemical observations being at odds with the expected geological expression of large-scale mantle upwelling. We re-evaluate the mechanisms responsible for generating extreme thermal gradients in the Narryer Terrane and propose that long-lived high crustal temperatures between ca. 2690 Ma and 2610 Ma were instead facilitated by elevated radiogenic heat production in thickened, highly differentiated ancient crust. Our findings suggest that mantle-derived magma input and new crustal addition may not be the only drivers for high- to ultra-high temperature metamorphism and cratonisation of ancient crustal blocks.