Developing highly efficient oxygen evolution reaction (OER) catalysts for electrolytic water splitting is urgently desirable but remains a challenge due to sluggish kinetic process of water oxidation. Herein, we report a one-step electrodeposition strategy to prepare Ni(OH)₂ modified with Ir single-atom catalysts (SACs) (Ir SACs/Ni(OH)₂) on an electrically conductive substrate of three dimensional (3D) hierarchical porous nickel foam (HP-NF) as efficient OER electrocatalyst. The HP-NF with abundant open pores can not only enable the full exposure of catalytically active sites but also facilitate the diffusion of electrolyte and release of gaseous oxygen produced. The optimal Ir SACs/Ni(OH)₂@HP-NF exhibits a remarkable catalytic performance and outstanding stability for the OER activity in 1.0 M KOH alkaline media, delivering a low overpotential of ~ 223 mV at a current density of 10 mA·cm⁻² and a low Tafel plot of 58 mV·dec⁻¹. Various characterizations together with control electrochemical experiments demonstrated that the superior activity and robust stability of Ir SACs/Ni(OH)₂@HP-NF for OER are originated from the highly distributed and exposed Ir SACs and 3D interconnected pores of HP-NF with high electric conductivity.