Venkatesh was a minister in the cabinet of Kiran Kumar Reddy, who resigned last week to protest the bifurcation of Andhra Pradesh.
After consulting his supporters, Venkatesh said he would join the TDP.
Venkatesh was considered a confidant of Kiran Reddy, who also quit the Congress and is planning to float a new regional party.
Venkatesh, an industrialist from Kurnool district of Rayalaseema region, was elected to the Andhra Pradesh assembly in 1999 and 2009. He had also formed a group to fight for protection of Rayalaseema’s rights.
It will be homecoming for Venkatesh, who quit the TDP in 2004 to join the Congress.
Two other former ministers – Ganta Srinivasa Rao and Erasu Pratap Reddy – are also likely to join the TDP, sources said.