Reported here is the discovery of a redox-neutral NiII /NiII catalytic cycle which is capable of the linear-selective hydroarylation of unactivated alkenes with arylboronic acids for the first time. This novel catalytic cycle, enabled by the use of an electron-rich diimine ligand, features broad substrate scope, and excellent functional-group and heterocycle compatibility under mild reaction conditions in the absence of additional oxidants and reductants. Mechanistic investigations using kinetic analysis and deuterium-labelling experiments revealed the protonation to be the rate-determining step in this redox-neutral catalysis, and the reversible chain-walking nature of the newly developed diimine-Ni catalyst.