Taking to micro-blogging site Twitter, Ms Lamba said, "The time has come to say 'Good Bye' to #AAP and to resign from the primary membership of the party. The past six years' journey was a great learning for me. Thanks to all."
The speculations of Alka Lamba quitting the party had been set off by her meeting with Congress president Sonia Gandhi on Tuesday.
Ms Lamba had been with the Congress for 20 years before AAP in 2013. She won the Delhi election from Chandni Chowk.