A novel 7-coordinated hydrated cobalt(II) ethylenediaminetetraacetate complex with hydrazinium cation, has been synthesized in aqueous medium and its composition has been assigned as (N2H5)2[Co(edta)(H2O)](H2O)2 on the basis of hydrazine, CHN and metal analyses and characterized by conductivity and magnetic measurement, UV-visible and infrared spectral and crystal studies. The thermal degradation studies reveal the presence of two types of water molecules viz., coordinated and lattice water molecules. Hydrazinium cation is present outside the coordination sphere as charge neutralizing species. X-ray single crystal structure reveals that the cobalt(II) ion is seven coordinated and edta4- act as a hexadentate chelating ligand. One water molecule occupies the seventh site resulting in the pentagonal bipyrimidal geometry. Hirshfeld surface analysis and fingerprint plots revealed influence of weak or non bonding interactions in crystal packing of complex. The DNA binding property of the complex with calf-thymus DNA has been investigated using electronic absorption spectrophotometry and the binding constant Kb calculated is in favour of strong interaction between the complex and DNA.