Two new Zintl compounds Ba₂Cd₂As₃ and Ba₂Cd₂Sb₃ have been synthesized and structurally characterized. They crystallize in a novel monoclinic structure type with the space group C2/m (no. 12), featuring polyanionic layers made of CdPn₄ tetrahedra (Pn = As, Sb) and homoatomic Pn–Pn bonds. The topological relationships between the structure of Ba₂Cd₂Sb₃ and those of BaCd₂Sb₂ (CaAl₂Si₂ type) and Ba₃Cd₂Sb₄ (own type) are discussed as well. Based on electronic structures calculations, carried out by the density-functional method, and resistivity measurements, pure Ba₂Cd₂As₃ is shown to be a small-gap semiconductor and pure Ba₂Cd₂Sb₃ to be a poor metal. The structures of the title compounds are amenable to doping on both cation and pnicogen sites, which could enable fine-tuning the transport properties, and make them promising materials for thermoelectric applications.