Congress president Sonia Gandhi on Tuesday evening declined to take up the prime minister's post.
Addressing the Congress Parliamentary Party at the Central Hall of Parliament, she said throughout the past six years that she has been in politics, one thing that has been clear to her is that the post of prime minister "is not important for me".
She said whenever she found herself in a position like this, she always followed her "inner voice. That voice tells me I must decline".
"I request you to accept my decision and recognise that I will not reconsider my decision," she told the Congress' newly elected MPs.
"My aim has always been to defend secularism. We have taken significant steps towards this goal," she said.
"We have won a successful battle but the war is yet to be won."
She said her foremost responsibility was to give the country a secular government that was strong and stable.
"As one of you and the president of Congress, I pledge to work with you for the Congress party towards our vision and principles."
The Congress MPs repeatedly surrounded her to persuade her to reverse the decision. They shouted that she should not bow to any pressure, to which Gandhi said that "there is no blackmail from any party. This is my inner voice and conscience".