Mitochondrial complex IV (Cytochrome c Oxidase) is the terminal enzyme of the electron transport chain. The electron transfer reaction is coupled to the vectorial translocation of protons across the inner membrane required for ATP synthesis. Human complex IV is composed of 3 subunits encoded by mitochondrial DNA (mtDNA) and 11 subunits encoded by the nuclear genome. In addition, numerous proteins known as assembly factors are required to coordinate the biogenesis of the complex but are not required for the enzymatic activity of the fully assembled enzyme. COA7 (Cytochrome c Oxidase Assembly Factor 7) is a complex IV assembly factor and mutations in the COA7 gene lead to mitochondrial disease. We used CRISPR/Cas9 gene editing in HEK293T cells, quantitative proteomic analysis, structural biology, and biochemical techniques to investigate the role of COA7 in complex IV assembly. Analysis of COA7 knockout cells revealed a total absence of complex IV, which were rescued upon expression of wild type COA7. Furthermore, metabolic labelling revealed a rapid turnover of the mtDNA encoded subunit COX2. Additionally, ectopic expression of COA7 harbouring mutations identified in patients with complex IV deficiency differed in their ability to complement the complex IV defect observed. The crystal structure of COA7 has been solved and refined to 2.3 Å resolution and includes 5 SEL1-like repeat domains, each with a helix-turn-helix fold, braced by a disulphide bond. Novel insights into the role of COA7 in Complex IV subunit maturation were obtained and are currently being investigated.