MSP Richard Leonard has confirmed that he hopes to succeed Kezia Dugdale as leader of the Scottish Labour Party.
In an article for the Sunday Mail, Mr Leonard said Scotland needed "a united Labour Party committed to real and bold change".
MSP Anas Sarwar, the party's health spokesman, is another frontrunner for the top job.
In the same paper, he said the contest would be about electing a leader who could serve as the next first minister.
Ms Dugdale announced on Tuesday that she was stepping down from the job with immediate effect.
She had been leader of Scottish Labour for two years, taking over from Jim Murphy after the disastrous 2015 general election campaign.
'Scottish Labour vision'
Mr Leonard is a former GMB trade union organiser who was elected to the Scottish Parliament in 2016. while Mr Sarwar is the party's Holyrood health spokesman as well as a former MP and deputy leader of the Scottish party.
Confirming his intention to stand in an article for the Sunday Mail, left-winger Mr Leonard said Scotland needed "a united Labour Party committed to real and bold change".
He praised the platform put forward by UK leader Jeremy Corbyn and called on the Scottish party to be more "audacious" and take chances to win back support.
Citing issues such as inequality, fuel poverty and public sector cuts, Mr Leonard said: "It is for these reasons that we need a distinctive Scottish Labour vision again - delivered with energy but also with conviction and credibility.
"That is why I decided to seek to be the next leader of the Scottish Labour Party - not simply to be the leader of a strong opposition, but to be the next Labour first minister."
He added: "It is now time to set out our vision of a more equal Scotland with full employment, funding quality public services, providing dignity for our OAPs and hope for our young."
He pledged to continue to "unflinchingly oppose" nationalism, adding: "Labour's strength is that we organise and represent people across the whole of these islands, as part of a worldwide movement."
'Radical policy platform'
Writing in the same newspaper, Mr Sarwar, who opposed Mr Corbyn in the last UK Labour leadership election, praised him and Ms Dugdale for helping to restore "a confidence in the party that we can win again".
He insisted that the Scottish leadership contest "will not be about the direction of the UK Labour Party" adding: "We are all united in our desire to elect Jeremy Corbyn as our next prime minister."
"It will be about electing a leader who can serve our country as the next first minister of Scotland," he said.
"I firmly believe Labour can achieve power again in both Holyrood and Westminster. We have a radical policy platform that stands in stark contrast to the SNP.
"The next Labour government in Scotland must fix the crisis in our health service.
"We will tackle the crisis in our schools, end the slash-and-burn approach to local government and build an economy rooted in fairness that equips our workforce for the challenges ahead."
He added: "The next Scottish Labour leader must unite our movement, continue to build confidence among voters and ensure the party are back where we should be - united, radical and in power."
Richard Leonard is a newcomer to parliamentary politics, having been elected to Holyrood on the Central Scotland list in 2016 - but he has been a voice on the left of the Scottish party for some time.
He has a strong trade union background with the GMB and the TUC, and could find himself the main pro-Corbyn candidate after Neil Findlay and Alex Rowley bowed out of the race before it even began.
He is an economy spokesman for the party at Holyrood, and was a key figure in drawing up the party's industrial strategy for Scotland.
Despite his lack of parliamentary experience Mr Leonard has a host of campaigning and party work behind him: he served on the Scottish Living Wage steering committee and is secretary of the Keir Hardie Society.
A former deputy leader of the party, when he was MP for Glasgow Central, Mr Sarwar was interim leader between the tenures of Johann Lamont and Jim Murphy in 2014.
He lost his Westminster seat in 2015, but was returned as an MSP for the Glasgow region the following year.
An experienced politician within the party, he has immediately taken up a prominent role in the group at Holyrood, acting as health spokesman.
Mr Sarwar could be pitched as something of a unity candidate, who could potentially seek support from both sides of the party's somewhat divided base in Scotland - the only part of the UK where Owen Smith beat Jeremy Corbyn in the 2016 leadership contest, at least in the popular vote of the membership.
He introduced Mr Corbyn at a recent rally in Glasgow, and could be positioning himself as a favourable choice for both moderates and the left.