Ruthenium-catalyzed meta-C(sp2)–H alkylations in the presence of secondary and tertiary alkyl halides are known to proceed through a radical pathway. However, the mechanism behind ruthenium-catalyzed ortho-C(sp2)–H alkylations remained thus far elusive. Now, we provide evidence for the ortho-alkylation to proceed via a one-electron radical pathway as supported by detailed experimental and computational DFT studies in terms of a ruthenium(II/III/IV) regime.