She was 89 and was being treated for the disease for some time, doctors said.
Ponnammal was a popular Congress MLA known for her simplicity and colloquial style of oration in the state assembly.
She was MLA from 1957-1967, 1984; 1989, 1991 and 1996. Except in 1996 when she won as Tamil Maanila Congress candidate, she was Congress MLA.
On Oct 28, Rahul Gandhi had called up the hospitalised legislator, enquired about her health and promised her all help.
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Condoling her death, TNCC President E V K S Elangovan hailed her contribution to the party.
"Hailing from the Dalit community, Ponnammal had dedicated her entire life for the growth of Congress. She was popular cutting across party lines and was affectionately addressed as Ponnammal Akka (elder sister)," he said.
Her demise was an irreparable loss to the party, he said in a statement, while recalling she had served seven terms as MLA of Nilakottai, Sholavandan and Palani over a period of 35 years.