Kezia Dugdale will pledge to “stand up to vested interests” as she launches her campaign to be the new leader of Scottish Labour.
The Lothian MSP insisted she would “shake things up” if she is elected into the top job.
Speaking ahead of her official campaign launch, Ms Dugdale said: “Now more than ever, Scotland needs a voice that will stand up to the vested interests.
“Scotland needs a strong opposition that asks tough questions, not a one-party state where every institution and every cause is linked to just one political party.
“That wouldn’t be good for Scotland. People need a champion against the cosy consensus in Scottish politics. I will be the anti-establishment voice Scottish society needs.”
The leadership contest, in which Ms Dugdale is running against fellow MSP Ken Macintosh, was sparked by the resignation of Jim Murphy after Labour was all but wiped out in Scotland in last month’s general election.
In a change from previous leadership contests, it will be a one member one vote ballot, while non-members can also register as supporters for £3, allowing them to take part in the election.
Ms Dugdale, who had served as deputy leader under Mr Murphy, is the favourite to win, despite only entering the Scottish Parliament in 2011.
She argued she is the “anti-establishment” candidate, saying: “We have a second-term Tory Government that now has a majority and nothing standing in its way.
“We have a SNP Government that has been in office for more than eight years and a First Minister who was elected to the Scottish Parliament more than fifteen years ago.
“We have institutions in this country that have become cosy with the status quo, even if they long ago ceased to deliver what’s best for the people of Scotland.”
But she vowed: “If I am elected leader I won’t stand for business as usual just because it’s inconvenient to say otherwise. I’m going to shake things up.
“Nothing will stand in the way of me tearing down the barriers that stop people fulfilling their potential. Under my leadership no-one will be in any doubt what the Labour Party stands for and who we stand with.
“Whether that’s women facing discrimination, parents whose kids need more support or a patient at the end of their tether because they can’t get the treatment they need from the NHS – I will speak up and speak out, no matter how unpopular it may be with those in the establishment it will upset.
“It won’t always be easy and it won’t always be popular, but I’m going to say the things too many people are scared to say in politics.”