Kevin Rudd supporter Martin Ferguson has resigned from Prime Minister Julia Gillard's cabinet.
Mr Ferguson, who was the minister for resources and energy, and for tourism, made the announcement in Canberra on Friday.
He's the second cabinet minister to stand down.
Fellow minister Chris Bowen resigned on Friday morning as minister for tertiary education.
Simon Crean was sacked on Thursday by Ms Gillard, who retained her leadership unopposed at a caucus meeting following Mr Rudd's decision not to stand.
Mr Ferguson said he had come to his decision after considerable thought and had informed Ms Gillard of his intention.
"I have a view it is the only honourable thing to do," he told reporters.
Mr Ferguson supported Mr Rudd's challenge in February last year, when he said he was worried about the direction of the party.
"For those reasons I would have voted for Kevin Rudd yesterday and Simon Crean (as deputy) to try and give this party a fresh start," he said.
"Unfortunately the events of yesterday were not what we have hoped for.
"The caucus has made the decision. I respect that decision."
Mr Ferguson said by resigning he was giving the prime minister and the ALP the opportunity to regain the Labor legacy of reform and embrace an approach which looked after all Australians.
"In doing so, seek the best position for the party I have been a member for 35 years to win the next election," he said.
He also gave credit to Labor stalwart Mr Crean, who had planned to run for the deputy leader spot and called for the spill.
"I thought what he did yesterday was courageous. It was about trying to give the party a fresh start," he said.
"For this reason, I would have supported him."
Mr Ferguson said Labor needed to "reclaim the legacy of the Hawke and Keating governments".
"(The legacy of) being a reforming government, " he said.
He hoped the current government had learned from the "mistakes" made during the development of mining tax debate in 2010, which in part led to Mr Rudd losing the leadership to Ms Gillard.
"You don't have to agree but you need to consult, argue it out, and work out a balance in society," he said.
"That is what I learned as a young trade union official."
Mr Ferguson is one of the only ministers to have remained in the same portfolio since the election of the Rudd government in 2007.
He said he would stand for election for his seat of Batman in September and remain in parliament for the full term if elected.
Mr Ferguson said he had spoken to very few people about his decision to stand down.
"This is a personal decision, and having made it I sat down today and re-read my first speech," he said.
The final paragraph was along these lines: "If I leave parliament with the same sense of dignity and standing that that my farther did, having left school at 13 gone on to be a bricklayer and deputy premier of NSW then I will have achieved something and maintained my dignity and honour."
He said it was not an easy decision to resign but it was honourable and he did not resile from it.