A national spokesperson of the Congress, she resigned from the party protesting against what she called some leaders' "dictating terms" and "suppressing" her.
She was with the DMK before joining the Congress in 2014.
Assembly polls are due in Tamil Nadu in the first half of the next year, and the BJP hopes the her induction will be a boost to it.
The BJP has long been a marginal force in the southern state where two Dravidian parties, the AIADMK and the DMK, have been the main contenders for power. KR DV DV