Scottish Labour will have a leadership election this summer after Kezia Dugdale and Ken Macintosh confirmed they will stand to succeed Jim Murphy.
Deputy leader Ms Dugdale, who is currently deputy leader, will launch her campaign next month when Mr Murphy formally steps down.
Announcing the move, the Lothian MSP said improving Scotland's education would be her top priority.
Mr Macintosh, the MSP for Eastwood, said he wanted to "rebuild trust and confidence in the party" by grassroots campaigning on bread and butter issues.
In a statement, Ms Dugdale said: "I am standing to be Scottish Labour Leader and I intend to transform my party for the good of my country.
"I will formally launch my campaign next month when the Scottish Executive Committee sets out the rules and timetable for the leadership contest. At that point there will be much more to say on how we must meet the challenge ahead.
"This is a moment when Scottish Labour must and will change. It's time for a new generation with a vision for the future of Scotland.
"Labour lost badly in the General Election. Nothing we can say or do will disguise that fact. The job of our next leader isn't to explain away that loss or find excuses - it's to understand why people were so reluctant to vote for us and find a way of regaining the trust of the people of Scotland.
"I do not underestimate the scale of the challenge Scottish Labour faces. But we've been the insurgent force before, pushing back against the political establishment and winning great victories and profound social change. We will be that force again. Our values are what we will carry forward with us - all the rest is baggage.
"We have a mountain to climb, but I believe I offer a fresh start for Scottish Labour. The great social change we fight for is not a partisan cause. I can be a unifying figure across our party and our country.
"As the daughter of two teachers I know the value of education. At its best it can transform the life chances of young people, no matter their background. The only way we can secure a fairer, brighter tomorrow for Scotland is by giving our young people a better start in life today. As Scottish Labour Leader that's what I would work for every single day."
Mr Macintosh said: "I am pleased to hear that Kezia has thrown her hat in the ring and that she agrees we have to have a contest. I am standing because I want to rebuild the trust and confidence in the Labour Party that seems to have drained away in recent years but that I have never lost. I believe we need to show by our very example that we care more about the people we represent than about politics or position."
The Eastwood MP stood unsuccessfully for the leadership in 2011.
He won the biggest share of support from grassroots party members, but lost out to Johann Lamont after she polled more strongly with parliamentarians and members of affiliated trade unions, under the party's three-way electoral college system.
Mr Macintosh is hoping the party moves to a one-member-one-vote system, a reform promised by Mr Murphy before he bows out.
Mr Murphy announced his decision to quit following Scottish Labour's crushing General Election defeat at the hands of the SNP.
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