A practical, efficient and green process for the preparation of losartan, an antihypertensive drug, has been developed with an overall yield of 58.6%. The key step is the synthesis of the two key intermediates 2-butyl-4-chloro-3H-imidazole-5-carbaldehyde (BCFI) and 2-cyano-4′-methyl biphenyl (OTBN). BCFI was synthesised from valeronitrile and acetyl chloride by three steps with an overall yield of 69%; OTBN was obtained in 86% yield by the coupling of o-chlorobenzonitrile with p-methylphenylmagnesium chloride in tetrahydrofuran in the presence of manganese chloride and chlorotrimethylsilane. The above route was successfully operated in at a pilot-plant operation.