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Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp³)−C and C(sp³)−O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni^IVcomplex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni^IIIcomplex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp³)−C(sp²) bond‐forming reductive elimination occurs from both centers, but the Ni^IIIcomplex reacts up to 300‐fold faster than the Ni^IV, depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO⁻), the Ni^IVcomplex exclusively undergoes C(sp³)−OAc bond formation, while the Ni^IIIanalogue forms the C(sp³)−C(sp²) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M−C(sp³) bonds, and thus their relative reactivity towards outer‐sphere S_N2‐type bond‐forming reactions.