Michael Marra and Joe Fagan will contest the Scottish Labour leadership after Monica Lennon failed to secure enough nominations to enter the race.
Anas Sarwar triggered the contest last month after he announced his intention to stand down as both Scottish leader and MSP to join Andy Burnham's government.
Sarwar's decision came after Labour finished joint second in May's Holyrood election, tied with Reform on 17 seats each.
Party members and affiliated supporters will vote for his replacement between 28 August and 17 September.
Nominations closed at 10:00 but only Marra and Fagan met the threshold required to be eligible.
After failing to get on the ballot Lennon accused Scottish Labour of being "stuck in the past".
Fagan said the leadership campaign was about "more than understanding what went wrong" for the party.
"It is about what Labour does next," he said.
"It is about respecting work, backing our communities and giving working people real power over the future, not asking them simply to live with decisions made elsewhere."
Marra said he was "humbled" to be on the ballot and looked forward to a "good spirited and comradely contest".
He added: "The next leader of Scottish Labour has a huge task: to unite our party, rediscover our soul and reconnect with Scotland.
The North East Scotland MSP offered his commiserations to Lennon, who he described as "one of the most formidable and effective campaigners the Labour movement has".
In a statement, Glasgow MSP Lennon said: "Scotland's young people deserve a Scottish Labour Party who will stand up to billionaires and the wealthy elite. Their future is on the line.
"Our planet is burning and hope is fading. Punching down on trans people and other minorities is not acceptable. Do better, lead with decency and act with courage."
Both Marra and South Scotland MSP Fagan - the two successful candidates - have expressed scepticism about recent attempts by the Scottish Parliament to make it easier for an individual to change their legally recognised sex.
Lennon added: "Our movement wants an inclusive, progressive and unapologetically socialist recovery."
Sarwar, who had led the party since 2021, declined to endorse a candidate during an Edinburgh Fringe event earlier this month.
But he warned the contenders and their teams against infighting.
Since his exit Dame Jackie Baillie has been acting leader of Scottish Labour.
As of last year, new rules prevent politicians from sitting at both Westminster and Holyrood at the same time.
There will not be a by-election for Sarwar's Holyrood seat as he was elected via the regional list.
Monica Lennon, who had been in the Scottish Parliament for a decade but was not re-elected in May, is the next name on the Glasgow list.
The winner of the leadership contest will be announced on 19 September.
Scottish Labour leader hopefuls warn against party divisions
Scottish Labour leader Anas Sarwar set to become a minister in Burnham's government
