Jackie Baillie told an audience in Glasgow today that she was opposed to a second referendum on independence and that Labour must instead position itself as "the party of devolution".
In a strongly worded attack on the SNP, the MSP for Dumbarton accused Nicola Sturgeon of leading a government that had overseen rising inequality and falling standards in the NHS.
"Why would you want to end the redistribution of wealth from the richest parts of the United Kingdom to Scotland," she said in a speech to supporters on Friday.
"That’s nationalism, and none of us in the Labour party, nobody in the trade union movement, no one truly committed to the funding of public services could support the vision of austerity set out by the SNP’s economic prospectus."
Scottish Labour faces yet another rebuilding effort after a disastrous performance at last year’s general election which saw the party lose all but one of its MPs.
It is also currently polling third out of the major parties ahead of the 2021 Scottish Parliamentary elections, a situation Ms Baillie branded “unacceptable”.
When asked what would constitute a good result for Labour at the next Holyrood vote, she did not make a prediction on an overall number of MSPs the party could win - but insisted it had to begin taking the attack to the SNP.
In her speech, she continued: "Are we going to spend the next few years repeating the SNP’s criticisms of us or are we going to get off our knees?
"Are we going to throw everything we’ve got at this arrogant, rotten SNP government or spend the time fighting amongst ourselves?"
Ms Baillie faces a challenge for the deputy leader role from Matt Kerr, a Glasgow councillor who yesterday faced criticism from his Labour colleagues after walking out of the local authority's annual budget meeting before a vote was held.
Votes for Scottish Labour have been in decline in recent years, with the party reduced to third place in the 2016 Holyrood elections.
Ms Baillie has challenged the party to shake up its electoral offering in order to win back support - while throwing her support behind current leader Richard Leonard.
The MSP was sacked by Mr Leonard from her front bench position in 2018, with the leader opting to take over the post himself - however, Ms Baillie told journalists she could "absolutely" work with the Labour leader.
In her speech to members - including MSPs Anas Sarwar, Daniel Johnson and James Kelly - Ms Baillie added: “If you think this is as good as it gets, if you think more of the same will do, then vote for the other guy.
“But if you think we can and must be better - better for our members, better for our movement and, most importantly, better for our country - then I hope I can count on your support.
“Because I am the real change candidate.”
She continued: “Next year’s campaign can’t be driven by a small group advocating more of the same - focused on ideology and the past rather than electability and our hopes for the future.
“We need to open our doors, rebuild and unite the Labour Party, look outwards, not inwards, and be ruthless in our intention to win.”
Responding to Ms Baillie’s comments, an SNP spokeswoman said: “The Labour party clearly hasn’t learned a thing if it thinks it can ignore democracy and deny people in Scotland a choice over our future.
“As long as Labour politicians think they can high-handedly lecture – and continue to back Boris Jonson instead of standing up for Scotland’s right to choose its own future – their support will continue to collapse.”