Kezia Dugdale will ask Labour members to back a new Act of Union at her party’s conference in Perth next year.
But the Scottish party leader will not give voters a say on any deal with a referendum.
At a speech to the IPPR in London, Ms Dugdale claimed her plan would “save” the Union.
She said: “I believe a new federal UK, with a strong Scotland able to carry forward a significant relationship with Europe, is what people across Scotland have voted for. It goes far to meet the dual mandates of the Scottish people, and gives us the best possible protection for our jobs and our economy.
“That is why on the first day of our party conference in Perth in February, I will ask the Scottish Labour Party to back this vision for a new Act of Union to establish a federal UK. This will restate Scottish Labour’s belief in the United Kingdom as a redistributive union and set a bold and radical new direction for Scotland and the UK.”
Ms Dugdale added: “There can no longer be any doubt that the UK – and everything that progressives are fighting for – is in peril.
“The Tories are to blame for that, and Ruth Davidson must never be allowed to forget that it is her party that nurtured the divisions that Nicola Sturgeon thrives upon.
“Our Union must be saved. We must heal our divided society. It is only Labour that can do that.”
The Scottish Labour leader also called for Holyrood to have responsibility for employment rights, including the ability to set a National Minimum Wage, although the UK government would set the minimum levels.
And she argued for powers over fishing and agricultural powers to come north of the border following Brexit.
Despite Ms Dudgale writing to the Prime Minister asking her to kick-start the convention, The Courier understands that no contact has been made with the Scottish Government.
SNP MSP Linda Fabiani said the proposals should be taken “with a pinch of salt”.
She added: “Labour have been promising a supercharged, powerhouse, federalism-max for years – and consistently failing to deliver it.”
The Scottish Conservatives accused Ms Dugdale of stoking constitutional uncertainty.
Chief whip John Lamont said: “On the day we are learning about massive failures in the SNP’s management of Scotland’s schools and NHS, Kezia Dugdale declares that what we need right now is even more constitutional upheaval.
“Surely 10 years of SNP government obsessing over the constitution has taught us that this is the wrong priority.”
Scottish Liberal Democrat leader Willie Rennie said the proposal showed there was “momentum building” for federalism.
He added: “Federalism is Scotland’s and the United Kingdom’s best chance to flourish.”
But Patrick Harvie, the Scottish Greens’ co-convener, said the proposals are unlikely to go ahead because the UK Government “appears unwilling to consider far more modest proposals”.
