Kezia Dugdale has rejected the view of union boss Len McCluskey, who said he cannot see Labour winning the General Election.
The Unite leader suggested winning 200 seats – nearly 30 fewer than in 2015 – would be a “successful” result for UK leader Jeremy Corbyn.
Ms Dugdale, the party’s leader in Scotland, said she defined success as “winning the election”.
She told BBC Radio Scotland: “I hope he is wrong, I want to see a Labour government across the whole of the United Kingdom, that’s what I’m spending every waking moment of my day campaigning for.”
She added: “I think he’s wrong, I hope he’s wrong.”
Asked what success would look like in Scotland where Labour had just one MP, Ms Dugdale said: “I am not going to put a number on it because I haven’t produced a list of target seats.
“I want to make progress in Scotland, I want to win more seats, I want to reduce the majority of SNP MPs in many other seats.
“The reality is in the vast majority of seats across Scotland’s central belt, it is the Labour Party that stands a very strong second to the SNP.”
Ms Dugdale was speaking ahead of a major campaign speech in Glasgow, where she will appeal to voters in Scotland who backed remaining in the EU and the UK.
She will say these voters are a “majority for change” and are not served by either the SNP or the Conservatives.
She will accuse the Tories and SNP of trying to hijack the result of the Scottish independence and EU referendums, and argue a vote for Labour rejects the “extremes” of both those parties.
Ms Dugdale will say: “In the face of some of the greatest challenges our country has ever faced, the choice at this election is being presented as one between a Scottish National Party with no programme to speak of and an emboldened Tory party that is pushing a hard Brexit at all costs.
“We cannot allow this to be the choice at this election – because it doesn’t represent what the vast majority of people in this country want.
“Across Scotland, people voted both to remain in the UK and remain in Europe.
“But our votes are being hijacked by Tory and SNP politicians who want to use how we voted in referendums and general elections to assume something about the kind of future we want to see.
“As a Labour Party, we put ourselves on the side of the vast majority of people across our country who rejected a hard Brexit and rejected independence.”