A process for the preparation of Irbesartan of formula (I) using the steps of: (i) reacting 4′ aminomethyl-2-cyano biphenyl of formula (VI) with 1-veleramido cyclopentane carboxylic acid of formula (V) in an organic solvent and in the presence of an acid, without activating the —COOH group of compound of formula (V) to give 1-(2′cyanobiphenyl-4-yl-methylaminocarbonyl)-1-pentanoylamino cyclopentane of formula (VII). converting the compound of formula (VII) obtained in step (i) to Irbesartan of formula (I) by reacting the compound of the formula (VII) with tributyl tin azide in o-xylene to give Irbesartan of formula (I).