Herein, [RuCl2(p-cymene)]2/[Cp*RhIIICl2]2-catalyzed direct alkylation of C(sp3)-H bond of 8-methylquinolines with olefins (acrylates, styrenes, and aliphatic) is reported. The alkylation also proceeds with other conjugated systems such as malemides and α,β-unsaturated ketones. The reaction is highly regioselective, forms only a linear product, and tolerates a variety of functional groups on quinoline and olefin moieties. Control experiments, deuterium labeling, and kinetic studies have been carried out for preliminary understanding of the reaction pathway. The reaction possibly proceeds through five-membered metallacycle under redox-neutral condition. Diversification of alkylated product and late-stage functionalization of ketoxime derivatives of (-)-santonin have also been carried out to demonstrate the applicability of the developed method.