Wendy Alexander has been officially named as Scottish Labour leader, beginning her new job by immediately setting out major party reforms.
She said she was determined to take Labour back to power, while criticising the SNP government for failing to deliver on election promises.
The Paisley North MSP was named as the sole nominee for the post last month.
Deputy First Minister Nicola Sturgeon said Ms Alexander had learned nothing from Labour's Scottish election defeat.
Speaking at an event in Glasgow, Ms Alexander, who succeeds former first minister Jack McConnell, said Scottish Labour had to change to win back the trust of the people and set out reforms which aimed to turn party supporters into party members.
She also said the party in Scotland would take the lead on issues that fell within the remit of Holyrood, adding: "At the same time, I don't expect the Westminster party to be trespassing into devolved affairs."
During her earlier acceptance speech, Ms Alexander said: "Under my leadership Scottish Labour will be a party of vision. A party of compassion. A party for all Scotland.
"It is Labour in Scotland, with its strong traditions of radical, progressive policies that has changed this country for the better."
Patrick Macdonald, a former chief executive of John Menzies, has been called in to review the Scottish party and bring forward proposals for reform, while a new think tank will seek to breathe fresh air into the policy-making process.
Turning her sights to the new Scottish Government, Ms Alexander, who was named leader-elect in August, said SNP pledges had been "broken, ditched, or cynically parked in the political long grass".
"Under my leadership, we will hold the SNP's minority administration to account for every broken promise and every pledge they fail to keep," said the former Scottish minister, who was backed by 41 of 46 MSPs to lead her party.
She claimed the SNP honeymoon seemed to be over, adding: "They have started to stall, bluster and backtrack on their election promises.
"Throughout their election campaign, none of the political parties in Scotland could work out where they were going to get the money to pay for their lavish promises."
Ms Sturgeon said Ms Alexander's "inward-looking" reform pledge was unambitious and "of virtually no interest to the people of Scotland".
"Labour did so little in eight years in Scottish government, and the SNP have already done so much in just over 120 days," she said.
"We are getting on with the job of governing in the Scottish interest, but Wendy's speech shows that Labour have a long way to go in learning the job of opposition."
Ms Alexander, whose MP brother Douglas is the international development secretary, also announced that Tom McCabe, the former finance minister, would work as an election campaign director.
She also appointed four Labour MSPs as regional campaign co-ordinators and said that Glasgow City Council leader Steven Purcell and Andy Kerr, the former health minister, would set up a new association of Scottish Labour councillors.
A new scheme, Ms Alexander added, would also be put in place to train party activists in modern campaigning techniques and the party would work with unions to attract new party members.