Scottish Labour leader Kezia Dugdale said she had faith in Jeremy Corbyn despite the party losing the Copeland by-election to the Conservatives.
The MSP was speaking ahead of her party's conference in Perth.
It opened just hours after Labour lost the Cumbrian constituency it had held for more than 80 years.
Ms Dugdale said she was "sad" at the loss but found solace that the party had re tained the Stoke-on-Trent Central seat in a second by-election.
Speaking to BBC Radio's Good Morning Scotland programme, the Scottish Labour leader said: "I have every faith in Jeremy Corbyn. He has now won two election contests within the Labour Party."
She agreed that the UK leader could "absolutely" take Labour to a general election victory.
Ms Dugdale added: "What people want to vote for is a united party.
"I am fully behind Jeremy Corbyn in his efforts to renew and build the Labour Party across the whole of the UK, just as I know he supports my efforts in Scotland where I have a long plan to renew the party's fortunes here."
The three-day conference will include speeches from Ms Dugdale, Mr Corbyn and London mayor Sadiq Khan.
Delegates will also debate policy resolutions on topics including federalism, the economy and local government, while looking ahead to May's council elections.
All of Holyrood's political parties are holding conferences in the coming weeks.
The theme of the Scottish Labour conference is "together we're stronger".
Facebook interview with Kezia Dugdale
The BBC's political correspondent Nick Eardley spoke to Scottish Labour leader Kezia Dugdale at her party's conference in Perth. Look back at what she had to say.
In her foreward in the conference handbook, Ms Dugdale said this was because "it's more important than ever that we work together to build Scotland for the future".
She said: "What people across Scotland want now, more than ever, is a plan for the future that puts their families, their job and the public services they rely on first.
"Employers and trade unions need stability and support. We don't need another divisive referendum.
"We can't allow our future to be shaped by the Tories or the SNP who only seek to divide our country."
Ms Dugdale will address delegates on Saturday, after Mr Khan and deputy UK leader Tom Watson.
Mr Corbyn and Shadow Scottish Secretary Dave Anderson will speak on Sunday, before Scottish deputy leader Alex Rowley closes the conference.
Mr Corbyn said a "strong, united and confident Labour party" was needed amid the "tumultuous and challenging" state of politics across the globe.
One of the first policies debated at the conference was Ms Dugdale's proposals for a federal UK.
Historic federalism vote
Delegates backed the motion for "a more federal UK" and a "People's Constitutional Convention, made up of citizens from across the United Kingdom".
The convention's findings will be reported before the next UK general election, scheduled to take place in 2020.
Scottish Labour deputy leader Alex Rowley said: "This is a historic vote as it commits Labour to Scotland remaining in a federal UK.
"Our call for a reformed UK isn't about constitutional tinkering - this is about meeting the demand for change.
"One message from the independence and EU referendums was that people wanted more control over their lives.
"That's why Labour's plan for a People's Constitutional Convention and a federal UK will transform where political and economic power will lie in our country.
Ahead of the federal debate, Ms Dugdale told BBC Radio Scotland that Mr Corbyn "fully supports" the people's constitutional convention.
Ms Dugdale added: "I have referred to it as an Act of Union and I understand Jeremy Corbyn might prefer to use other words because he has to examine the case for powers across the whole of the UK - not just between Scotland and Westminster, he has got to consider the needs of Wales, the needs of London, the needs of the north of England."
She went on: "We shouldn't obsess about the words - what there is underneath all of this is a principle and a great idea of how we can heal our divided country, bring people back together, unite our country, focus on the future and all the challenges that we face."