He addressed a letter to top leader Sonia Gandhi explaining the reasons for his resignation.
In a setback to the Congress in Telangana, senior party leader and former minister Marri Shashidhar Reddy, son of former Chief Minister of undivided Andhra Pradesh Marri Channa Reddy, quit the party on Tuesday.
Shashidhar Reddy, who had been a loyal Congressman for several decades and even headed a 'Congress Loyalists Forum' of Telangana Congress leaders, sent his resignation to AICC president Mallikarjun Kharge.
He addressed a letter to top leader Sonia Gandhi explaining the reasons for his resignation.
In the letter, he wrote about the allegedly growing influence of money in party affairs, its failure in effectively taking on the ruling TRS in Telangana and the poor functioning of AICC in-charges and PCC presidents.
Recalling the long association he and his late father have had with the Congress since the party's election symbol was a "pair of bullocks" followed by "cow and calf" in the 1960s, he said it was on the advice of his father that later Indira Gandhi had opted for the "hand" symbol.
He alleged that the influence of money was growing in the party affairs.
"They (the AICC in-charges) have consistently failed to function as representatives of the high command and were playing along to promote the personal agenda of successive PCC presidents and failed to protect the party's interest. So much so, it is impossible to believe that money has not been a driving force," he said in the letter to Sonia Gandhi.
"There are enough instances that give credence to suspicions that it was not just the AICC in-charge of Telangana, Manickam Tagore, who has been the recipient of largesse from PCC president Revanth Reddy, but also KC Venugopal, the key AICC General Secretary (Organisation). I am saying this with all responsibility, though I have not seen money being exchanged between them," he said.
Crediting Sonia Gandhi for the formation of Telangana, Shashidhar Reddy said the Congress in the state, however, could not take advantage of it.
There has been a steady decline in the Congress' electoral performance since 2014 and the party has missed the opportunities to take on the TRS and challenge its misdeeds, he said.
The ruling TRS was allowed to go "scot-free" and there was a widespread feeling that some leaders at the helm of Congress were compromised, and as a result, people gradually started losing confidence in the party's leadership, he claimed.
Shashidhar Reddy further alleged that successive AICC in-charges have done a great disservice to the party beginning with Digvijay Singh and that views of partymen like him to appoint a loyalist as PCC president were ignored.
He also wrote about the alleged failure of state Congress president Revanth Reddy in building the party organisation and the latter's undesirable attitude towards some senior leaders and issues.
"For me, it is Telangana first right now. Since Congress has miserably failed to play its role as the main opposition with commitment to protect the people's interests, I wish to bid farewell to the party and pursue viable options and contribute to save the people from the clutches of the ruling TRS party," he said.
He thanked the Congress for making him a minister when late PV Narasimha Rao was the Prime Minister and the Congress president, and also for appointing him to the post of vice-chairman of National Disaster Management Authority (NDMA) during the UPA regime.
Shashidhar Reddy said he would join the BJP on November 25 in Delhi.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)