One pot synthesis of benzimidazole from o-nitroaniline was achieved by using CuFe2O4 as a catalyst. It comprises the reduction of o-nitroaniline followed by cyclization, without using an external H-2 source. The thermal decomposition of DMF in situ generates CO, which undergo water gas shift reaction (WGSR) in the presence of CuFe2O4 to produce hydrogen. It reduces -NO2 (nitroaniline) to -NH2 (o-phenylenediamine, OPD). The further cyclisation of OPD to benzimidazole was done by using DMF as a C1 source, in the presence of magnetically separable CuFe2O4 as catalyst. This is the first example of its kind being reported here. The catalyst was prepared by a simple hydrothermal method, with an environmentally benign starting material. CuFe2O4 is cheap and reusable having very low toxicity. This is an economical synthetic protocol for benzimidazole from o-nitroaniline with 100% conversion in 12 h with 97.5% selectivity. A variety of o-nitroaniline substrates were studied using the protocol with excellent conversion and selectivity in each case.