The  lunar basalt samples returned by the Chang’e-5 mission erupted about  2.0 billion years ago during the late period of the Moon’s secular  cooling. The conditions of mantle melting in the source region and the  migration of magma through the thick lithosphere that led to this  relatively late lunar volcanism remain open questions. Here we combine  quantitative textural analyses of Chang’e-5 basaltic clasts, diffusion  chronometry, clinopyroxene geothermobarometers and crystallization  simulations to establish a holistic picture of the dynamic  magmatic–thermal evolution of these young lunar basalts. We find that  the Chang’e-5 basalts originated from an olivine-bearing pyroxenite  mantle source (10–13 kbar or 250 ± 50 km; 1,350 ± 50 °C), similar to  Apollo 12 low-Ti basalts. We propose these magmas then ascended through  the plumbing system and accumulated mainly at the top of the  lithospheric mantle (~2–5 kbar or 40–100 km, 1,150 ± 50 °C), where they  stalled at least several hundred days and evolved via high-degree  fractional crystallization. Finally, the remaining evolved melts erupted  rapidly onto the surface over several days. Our magmatic–thermal  evolution model indicates abundant low-solidus pyroxenites in the mantle  source with a slightly enhanced inventory of radioactive elements can  explain the prolonged, but declining, lunar volcanism up to about 2  billion years ago and beyond.