Alka Lamba, a former national president of the Congress student wing, Thursday quit the Congress to end a 20-year association and sought admission in the Aam Aadmi Party (AAP).
"Time to say goodbye to Cong(ress) and its leadership after spending 20 years with them," Lamba tweeted. "Lastly I would say 'thanks' to Congress president Sonia Gandhi."
The 38-year-old Lamba went over to the office of the AAP, which will form a government in Delhi Saturday, and sought its membership.
AAP leader Yogendra Yadav said she was told that she should fill up a membership form and serve as an "active volunteer" for four months before the party decides if she can be enrolled or not.
Lamba became the president of the Delhi University Students Union in 1995, and was elected national president of the National Students Union of India (NSUI) two years later.
She contested against Bharatiya Janata Party leader Madanlal Khurana in the 2003 Delhi assembly elections on Congress ticket and lost.