Anas Sarwar and Monica Lennon will face off to become the leader of Scottish Labour after nominations closed on Tuesday.
The pair were both able to gain at least four nominations each from MSPs or Labour’s sole Scottish MP in order to trigger the contest.
The party’s ruling body has set out a condensed timetable which will see a new leader appointed to succeed Richard Leonard by the end of next month, more than eight weeks before the Holyrood elections.
Mr Sarwar has claimed to have won the support of 15 of Scottish Labour’s 23 MSPs, as well as Edinburgh MP Ian Murray and more than 70 councillors.
After nominations closed, he said: “The hard graft starts here.”
Leadership hustings will take place between Wednesday and February 9, the same day the voting opens.
In the early days of the campaign, Scotland’s constitutional future has become one of its key issues, with Ms Lennon saying the party should not move to block another vote on independence.
She told the BBC: “I don’t believe in Scottish independence but I do understand people maybe have frustrations, things are not settled, and I’m not in politics to tell people what they can’t have. I’ll always respect democracy.
“We have to find out why this is such a polarising issue in Scotland, we can’t just wish it away.”
Meanwhile, Mr Sarwar, a steadfast opponent of Scottish independence and the party’s constitution spokesman under Richard Leonard, said the next parliamentary term should be used to recover from the Covid-19 pandemic.
He told the Daily Record on Tuesday: “I do not support an independence referendum in the next parliament. I support the next parliament being a Covid recovery parliament.”
When asked how the party can win back support from the SNP, he said it should “be true to our principles, we’ve got to say what we believe and why we believe it, and hope to win people back on that argument”.