K Hareeswar Reddy, a TDP veteran from Ranga Reddy district, joined TRS in the presence of Rao at a rally in his assembly constituency Parigi.
Reddy had been staying away from TDP for quite some time on account of its 'ambivalent' stance on the separate statehood issue.
At the rally, the TRS president hit out at former Chief Ministers N Chandrababu Naidu and the late Y S Rajasekhara Reddy for doing injustice to Telangana. "The two exploited Telangana for political gains," Rao alleged.
Rao also reiterated that the ruling Congress did not accept separate Telangana demand despite an offer to merge his party with Congress, and added that the separate state should now be achieved by "commanding" and not by requesting.
Telangana should have its strong political identity to make Centre accept the statehood demand, he said.
Rao also said the Kiran Kumar Reddy government was on edge in the wake of withdrawal of support by MIM.
"The government would fall if only five MLAs switched sides," Rao claimed.