An efficient manganese(II)-catalyzed oxidative radical cascade reaction was developed for the modular synthesis of multi-substituted isoquinolines from easily accessible vinyl isocyanides and hydrazines. Pyrrolo[1,2-a]quinoxalines and phenanthridines could also be afforded efficiently by this method and a wide range of alkyl, (hetero)aryl and alkoxycarbonyl substitutions could be easily introduced.