YS Sharmila, founder of YSR Telangana Party, joined the Congress party on Thursday. She had arrived in the national capital late on Wednesday.
At the event, she also announced the merger of her YSR Telangana Congress with the Congress and said she would fulfill any responsibility given to her.
Party chief Mallikarjun Kharge and former party president Rahul Gandhi were also present at the event
Sharmila is the daughter of the former chief minister of undivided Andhra Pradesh, the late YS Rajasekhara Reddy, and the younger sister of Andhra Pradesh Chief Minister YS Jagan Mohan Reddy.
She said it was her father's dream to see Rahul Gandhi as the Prime Minister and she would be happy to contribute to it.
Upon her arrival at the Delhi airport, when Sharmila was asked whether she was joining the Congress, she told reporters, "Yes, looks like it".
On Tuesday, Sharmila in Hyderabad had said she and other leaders would meet the top leadership of the Congress, including AICC president Mallikarjun Kharge and Rahul Gandhi, and make a "crucial" announcement in Delhi.
During the recent assembly polls in Telangana, Sharmila had announced her support to the Congress to end the alleged corrupt and anti-people rule of the BRS led by K Chandrasekhar Rao