Stem cell fate decisions-whether to self-renew, differentiate, or senesce-are inextricably linked to the metabolic identity and quality-control status of mitochondria. The ubiquitin-proteasome system and selective autophagy pathways assemble into an integrated surveillance network at the mitochondrial outer membrane that gauges organelle health, sculpts morphology, and transduces metabolic information into lineage-determining transcriptional programmes. This Review examines how the ubiquitination machinery-spanning the canonical PINK1-Parkin axis and non-Parkin E3 ligases including MARCH5, MUL1, and the emerging Cullin-RING component RBX2-orchestrates outer-membrane protein degradation, mitochondria-derived vesicle biogenesis, and the balance between fusion and fission. We discuss how these post-translational events govern stem cell identity across haematopoietic, muscle, neural, mesenchymal, and pluripotent compartments. Recent 2024-2025 advances include an Nicotinamide Adenine Dinucleotide (NAD+)-dependent metabolic checkpoint governing haematopoietic stem cell activation and aging, the crystallographic resolution of USP30 inhibitor binding, molecular glue activators that allosterically enhance Parkin RING-domain activity, ClpP-based mitochondria-targeted PROTAC platforms, and HIF-1α/BNIP3-mediated pharmacological rejuvenation of aged mesenchymal stem cells. We further discuss the WAC-PINK1-Parkin axis in mesenchymal stem cell aging, the bidirectional interplay between reactive oxygen species and E3 ligase activity, and the ACC1-FIS1 ubiquitination axis. Finally, we consider the cell-type-specific calibration of mitochondrial ubiquitination as a unifying principle for precision therapeutics and the inverted quality-control logic exploited by cancer stem cells. We propose that the cell-type-specific calibration of mitochondrial ubiquitination-whereby identical molecular events carry divergent functional consequences across stem cell compartments-offers a unifying framework for precision therapeutics.
