The development of organometallic catalysis has greatly expanded the synthetic chemist toolbox compared to that only exploiting "classical" organic chemistry. Although more widely used in organic solvents, metal-based catalysts have also emerged as efficient tools for developing organic transformations in water, thus paving the way for further development of bio-compatible reactions. However, performing metal-catalysed reactions within living cells or organisms induces additional constraints to the design of reactions and catalysts. In particular, metal complexes must exhibit good efficiency in complex aqueous media at low concentrations, good cell specificity, good cellular uptake and low toxicity. In this perspective, we focus on the presentation of discrete metal complexes that catalyse or photocatalyse reactions within living cells or living organisms. We describe the different reaction designs that have proved to be successful in these conditions which involve very few metals (Ir, Pd, Ru, Pt, Cu, Au, Fe) and range from in cellulo deprotection/decaging/activation of fluorophores, drugs, proteins and DNA, to in cellulo synthesis of active molecules, protein and organelle labelling. We also present developments of bio-compatible photo-activatable catalysts which is a very recent emerging area of research and some perspectives in the field.