In the title compound, C(19)H(18)N(3) (+)·Br(-), both the allyl and cyano-phenyl groups are approximately perpendicular to the central benzimidazole unit, making dihedral angles of 89.7 (2) and 85.09 (13)°, respectively. The crystal packing is dominated by C-H⋯Br inter-actions, with each anion inter-acting with five neighboring cations.