Highlights • Identification of a 3 MDa complex of the inner mitochondrial membrane • Mitochondrial multifunctional assembly (MIMAS) combines respiratory assembly and metabolism • MIMAS integrity requires the non-bilayer phospholipid phosphatidylethanolamine • The protein-lipid mega-assembly MIMAS functions as a biogenesis and metabolic platform Summary The mitochondrial inner membrane plays central roles in bioenergetics and metabolism and contains several established membrane protein complexes.