Ramanathi originates at an altitude of 1720m above the mean sea level, from the eastern slopes of the Western Ghats, in the north western corner of Ambasamudram taluk. After its journey downhill, the river joins with its tributary Jambunathi, at a distance of 8 km from the Melakadayam village. Following its merger with the Jambunathi, the river is known as the Veeranathi or Varahanathi. It joins the Gadananathi near the village Kila Ambur and finally empties into the river Tamiraparani near Thiruppudaimaruthur.
In the earlier part of its course, Ramanathi branches off into two, the Ramanathi Vadakal and the Ramanathi 'thenkal' which later rejoins at the juncture of its confluence with the Jambunathi. Extensively used for irrigation purposes, these branches have 8 dams constructed across them.