Her deputy, Dr Shane Reti, is the interim leader of the party after a dramatic 15 hours.
Late last night, Collins released a statement informing the press Simon Bridges was being demoted following a complaint around a serious misconduct allegation.
It is understood that MP is Jacqui Dean and the comment was allegedly made in front of Dean in 2017.
Bridges was stripped of his portfolios, prompting him to remark it was "truly desperate stuff" from Collins outside Parliament this morning.
Collins tweeted this afternoon she is now "just the MP for Papakura again", stating it was a "privilege to take over the leadership of the National Party during the worst times".
"It has taken huge stamina and resolve."
Collins said leadership was difficult due to a variety of factors.
"I knew when I was confided in by a female colleague regarding her allegation of serious misconduct against a senior colleague, that I would likely lose the leadership by taking the matter so seriously.
"If I hadn’t, then I felt that I wouldn’t deserve the role."
Collins said she did not "ask for the allegation to be given to me".
"I am proud of the support I received from Dr Shane Reti, a man of principle, and I will continue to advocate, not only for Papakura, but for those who have no voice."
She finished by saying she would not miss the gruelling media schedule.
Collins also confirmed on Twitter she would stand in the next election in Papakura.
Public relations consultant and former National press secretary Ben Thomas said the situation proved Collins would “stop at nothing” for her political advancement.
While Collins isn’t showing any sign she would resign, Thomas said it was very unlikely she’d remain in a senior position within the party under any new leader.
“The circumstances in which she tried to kneecap Simon Bridges today, I note from her tweets that she’s continuing to say it’s a point of principle.
“The facts certainly don’t seem to bear out the very serious allegations she made,” Thomas said.
Collins had held the position of leader for more than a year.
Collins was elected leader in July 2020, following Todd Muller’s resignation after 53 days in charge after he rolled Bridges.