Metal exsolution engineering has been regarded as a promising strategy for activating intrinsically inert perovskite oxide catalysts toward efficient oxygen evolution reaction. Traditional metal exsolution processes on perovskites are often achieved by using the reducing hydrogen gas; however, this is not effective for the relatively stable phase, such as Ruddlesden–Popper perovskite oxides. To address this issue, triphenylphosphine is proposed to be a reduction promotor for accelerating the reduction and migration of the target metal atoms, aiming to achieve the effective exsolution of metallic species from Ruddlesden–Popper-type parent perovskites. Upon oxygen evolution reaction, these exsolved metallic aggregates are reconstructed into oxyhydroxides as the real active centers. After further modification by low-percentage iridium oxide nanoclusters, the optimal catalyst delivered an overpotential as low as 305 mV for generating the density of 10 mA cm⁻², outperforming these reported noble metal-containing perovskite-based alkaline oxygen evolution reaction electrocatalysts. This work provides a potential approach to activate catalytically inert oxides through promoting surface metal exsolution and explores a novel class of Ruddlesden–Popper-type oxides for electrocatalytic applications.