Rebecca White is stepping aside, confirming she will not recontest the leadership of the Tasmanian Labor Party.
Instead, she has endorsed the party's existing Treasury spokesperson David O'Byrne for the position.
Ms White previously said she wanted to remain party leader after the election.
However, on Saturday afternoon with husband Rodney and daughter Mia by her side, Ms White said it was time for the party to see change to allow them to focus on winning the next election.
"It's been such an honour over the last four years to lead the Labor party, and I hope through that time I've done it with integrity and purpose," she said.
"I've felt so well supported by the community and I'd like to thank everybody for their engagement with me over the last four years and the constructive contributions that our community has made to support me both in the leadership role and the Tasmanian Labor party."
Ms White said her pregnancy did not play a part in her decision.
"When I took on the leadership in 2017, Rod and my daughter Mia was just shy of four months old and at no time did my age or my gender or our young family impact the decision of whether or not I should be leader," she said
"I think that's testament to the culture of the Labor party and I'd also like to make it really clear now that I'm not standing aside as the leader because of my pregnancy.
"I want young girls and women everywhere to know that they can achieve anything and they should walk through doors when they open or they should kick the door down if they have to.
I want young girls and women everywhere to know that they can achieve anything and they should walk through doors when they open or they should kick the door down if they have to.- Rebecca White
"I think that this change is necessary to the chances for the Labor party at the next election, it's about changing a range of things that we do as a Labor party right across the state."
Ms White said the leadership shake-up would be the first of many changes needed within the party.
"There's no doubt that after the election loss we needed to reflect on what had occurred, and I see the change in leadership for the state parliamentary Labor party as a part of the change that is now necessary for the Labor party, so we can become more competitive to win the next election," she said.
"Changing the leader of the parliamentary Labor party is just one part of the change that needs to occur now, which is necessary to improve the decision making and governance of the parliamentary party more broadly, to ensure that we are reflective of the community and we can build a strong Labor party to take to the next election."
Ms White said she had mixed emotions about the decision.
"I am very privileged and grateful to all of the support I have had as the leader of the Labor party, but I'm also very sad that I can't take the party forward because there is so much that we have to do together," she said.
"I will continue to stay on as a member of parliament and I will continue to contribute as best I can because I believe absolutely that only a Labor government can deliver better lives for Tasmanians."
Greens leader Cassy O'Connor wished Ms White well, and a "less politically stressful life as a Labor MP".
"After four years at the helm of Labor and a gruelling snap election, Rebecca has earned a break," she said.
"While there was plenty to admire in Ms White as Labor Leader, her decision to walk away from Labor's principled pokies policy, and refusal to work with the Greens, point to old Lennon Labor.
"For the sake of all Tasmanians, I hope this will be a fresh start for Labor."
Premier Peter Gutwein's message was short and sweet.
"On behalf of the Tasmanian Liberal government, I would like to wish Rebecca White well after her resignation as leader of the Tasmanian Labor party," he said.
"While Ms White and I have not always seen eye to eye, I respect her for her hard work and wish her all the best for the future."
Ms White has endorsed the party's existing treasury spokesperson David O'Byrne for the top job.
"The only names that we've heard so far [those interested in becoming leader] are of course David and Shane [Broad], great colleagues of mine and I think they're both outstanding parliamentary contributors and terrific local members," she said.
"I've made it clear to David that I'll provide him my support, and I know that as a caucus we'll come together next week and we'll have this conversation, it's unclear yet whether there'll be any ballot."
Both Dr Broad and Mr O'Byrne were contacted for comment.
Dr Broad said he was having discussions and considering his options.
It has long been speculated that Mr O'Byrne was gunning for party leadership, however he did not respond by deadline.
The Labor caucus are set to meet next week.
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