Deuterated molecules feature important biological activities and pharmacokinetic properties for the design of pharmaceuticals. Radical cyclization cascades involving the deuteration of alkenes to form heterocyclic compounds have rarely been reported. Herein, a deuterium addition cascade cyano insertion/cyclization of N-arylacrylamides to synthesize deuterated phenanthridines is described. Cheap Fe(NO₃)₃·9H₂O enables the generation of a deuterium radical from NaBD₄in situ. These reactions proceed under mild conditions in a short time and a variety of functional groups are well tolerated.