Michael Marra has called his election as the new leader of Scottish Labour a "singular honour".
The North East Scotland MSP, who has been the party's finance spokesperson, defeated South Scotland MSP Joe Fagan in a contest voted on by thousands of members.
Mr Marra replaces Anas Sarwar, who stood down from the top job after the party suffered its worst result in the history of devolution in May's Scottish parliament elections.
It returned just 17 MSPs as it lost its fifth consecutive contest in Holyrood.
Mr Sarwar quit his role in July and joined the House of Lords, becoming a trade minister in Andy Burnham's government in Westminster.
Voting in the contest opened on 28 August, with Mr Marra and Mr Fagan taking part in a series of hustings across the country in a bid to woo party members.
There were a total of 6,751 votes cast (a membership turnout of 49.43%), with Mr Marra winning 4,266 votes while Mr Fagan achieved 2,485 votes.
Reacting to his victory, Mr Marra said: "To be entrusted with the leadership of our Scottish Labour party is a singular honour and a great responsibility."
"I'm very grateful for your trust and I take on the duty of advancing our cause of a fairer, more equal Scotland with all that I can possibly give."
Mr Marra also said: "I want Scottish Labour to become a genuinely national party again, rooted in every part of Scotland, open to everyone and capable of bringing communities together."
He said he had three priorities over the next year - "1. Open up our party and reconnect it with Scotland. 2. Recover Labour's purpose and start building that programme for the future. 3. Deliver change now."
Mr Marra also thanked his predecessor, saying Mr Sarwar "took over a party that was out on its feet".
"He strapped on his boots and he took us to a place where we led the charge and kicking the Tories out of Downing Street."
Mr Marra has insisted Scottish Labour is still a "significant force" in Scottish politics despite this year's election results.
The number of MSPs elected for the party has declined in every Holyrood election since devolution, falling to just 17 after May's vote. The result meant it was the joint second-largest party, tied with Reform UK.
On the question of Scottish independence, Mr Marra has said there is a "route" to a second referendum through "creating a settled will of the Scottish people".
But he said comparing Scotland to Northern Ireland - which has a legal trigger for a referendum - was "dangerous".
Earlier this month, the prime minister said a vote on Scottish independence could be held if there was a "clear consensus" north of the border for it, but a letter later sent to First Minister John Swinney said a referendum remained "off limits".
SNP leader Mr Swinney has pushed for a referendum to be held within the next five years.
This week he met the leaders of Plaid Cymru and Sinn Fein during what they described as a "landmark" summit aimed at pressuring Downing Street into holding independence referendums.
Ahead of polls closing in the leadership race on Thursday, Mr Marra said he would practice what he described as "open-door politics" both within the party and Holyrood.
In engaging with party members, Mr Marra has said he plans to hold a series of regional meetings, where he will, effectively, take his lead from those on the ground.
But he also said he would be open to working with other parties and the Scottish government.
While Mr Marra claimed he has always been willing to work with the government, he was part of the Labour group which chose to abstain on the budget vote in each of the past two years, effectively waving through the government's plans without gaining anything in return.
Also, he claimed that for both the country and the party, education has been less of a priority than it should be, as he pledged to put it "at the heart of our politics".
(c) Sky News 2026: Michael Marra named new leader of Scottish Labour
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