Labour's Jeremy Corbyn will insist the party is "alive and kicking" and on the cusp of making significant gains in Scotland as he addresses activists in Dundee.
The UK leader will rally the party faithful by declaring "Labour in Scotland is back" in a keynote speech to the Scottish Labour Party conference.
He is expected to set out the benefits of a "Labour Brexit" to Scotland but, alongside Scottish leader Richard Leonard, will face continued pressure from pro-remain delegates to back permanent single market membership.
Mr Corbyn will say: "This time last year there were more than a few people in the media who had written the Labour Party off. In Scotland we were told that Labour was dying.
"The truth is that we very much are alive and kicking. Labour in Scotland is back.
"Led by Richard Leonard - who has already proven to be an excellent leader of Scottish Labour - we are making Labour's voice heard for a radically fairer society."
Mr Corbyn will say Labour, which gained six Scottish seats in the snap general election last year, is "on the cusp" of winning in about 20 more.
He added: "Of course I know that we didn't quite win. But we are no longer just an opposition. We are a party preparing to go into government."
Mr Corbyn, who backs a UK-EU customs union but not permanent membership of the EU single market, will say that the Tories' plans for Brexit are in "chaos".
He is expected to say: "At one of the most important times for our country in its history, we have a divided Government that has no clear idea of what it's doing, what it wants, or where it's going.
"As Theresa May has now admitted, under her plans for a reckless Tory Brexit the UK risks losing access to European markets.
"Make no mistake about it, reduced access to European markets means fewer economic opportunities for people in the UK.
"This is why we need a Labour government to take the reins from the free market ideologues who want to use Brexit to sign a race-to-the-bottom trade deal with Trump's America and turn the UK into a deregulated offshore tax haven.
"Instead, Labour will bring new common sense into the heart of government and help bring about a society that truly does work for all.
"With the Tories obsessed with elite deals in Westminster and Brussels, and the SNP obsessed with elite deals in Edinburgh, Labour is the only party focusing on the issues that matter to people in their everyday lives."
Brexit is due to be debated at the three-day conference during an hour-long slot on Sunday morning, with both Mr Corbyn and Mr Leonard facing calls for the party to back permanent single market membership.
A new Scottish Labour for the Single Market group is backed by Edinburgh South MP Ian Murray, former Scottish party leader Kezia Dugdale and MEP Catherine Stihler, while several constituency labour parties have submitted motions backing permanent membership.
SNP MSP George Adam said: "Labour remain hopelessly split over Brexit - and Richard Leonard's support for the Tories' extreme Brexit outside the single market will be the elephant in the room.
"That stance is alienating huge numbers of Labour supporters and members across Scotland and the rest of the UK."