A novel synthetic approach toward benzo[a]carbazoles or 6-amino benzo[a]carbazoles containing an unprotected NH unit through Rh(III)-catalyzed cascade reactions of 2-arylindoles or 2-arylindole-3-carbonitriles with α-diazo carbonyl compounds has been established. To our knowledge, this is the first example in which the NH unit of indole is used as a directing group for an intramolecular C(sp²)–H bond functionalization to give benzo[a]carbazole derivatives. Notably, this method features easily obtainable substrates, good functional group tolerance, excellent regio-selectivity, and high atom-efficiency.