On Tuesday, Sahra Wagenknecht, 48, will launch the grassroots project which borrows from the campaigns of British Labour's Jeremy Corbyn, French Socialist Jean-Luc Melenchon and US Democrat Bernie Sanders.
Its aim is to energise followers of her far-left Die Linke party, the centre-left Social Democrats (SPD) and ecologist Greens – but also to win back disenchanted working-class voters who have drifted to far-right protest parties.
Its website launched in mid-August cites reggae singer Bob Marley's chant “get up, stand up!” and declares boldly that “no politician, no party will solve our problems if we don't do it ourselves”.
Tens of thousands have signed up online to join the fight for secure jobs and pensions, good education, protecting the environment, disarmament and “a true democracy not ruled by banks, corporations and lobbyists”.
The jury is still out on whether it will spark a political revolution or quickly fizzle out.
Unsurprisingly, party leaders across the left, including Wagenknecht's own comrades at Die Linke, have rejected the Stand Up (“Aufstehen”) guerilla campaign as divisive and unhelpful.
The leader of the SPD, Germany's traditional labour party, Andrea Nahles, quipped that she “wasn't losing any sleep over it”.
Others have greeted the effort to re-energise the left as a challenge to Merkel's centrist coalition government and the rise of the far-right Alternative for Germany (AfD).
News weekly Der Spiegel said that, after populist anger over immigration swept the AfD into parliament last year, “it is high time to launch a movement of rallying the left”.
Open borders unrealistic
But even backers of the idea have wondered whether it is being led by the right people.
Wagenknecht, 48 and hailing from the former communist East Germany, is a lawmaker and polarising TV talk show star, married to a firebrand leftist SPD defector, ex-finance minister Oskar Lafontaine.
Known as rhetorically brilliant but awkward with voters, she is frequently critical of the EU and defends Vladimir Putin's Russia.
She argues that the SPD has sold out its principles and failed to fight back against unbridled capitalism and Merkel's neo-liberal” policies.
As Germany has absorbed a mass influx of migrants and refugees, which has sparked a far-right backlash, Wagenknecht has also broken with the left's traditional orthodoxy on immigration.
“The idea of 'open borders for all' is unrealistic,” she said in a recent interview.
“If the core concern of leftist politics is to represent the disadvantaged, then the no-borders position is the opposite of being on the left.
“All successes in restraining and regulating capitalism have been achieved within individual states, and states have borders.”
Berlin political scientist Dieter Rucht said such views may indeed “please some of the AfD's voters”, predicting success for the new movement “at least in the short term”.
Left and right meet
The idea of a cross-party leftist alliance has repeatedly come up and been dismissed – in large part because of Die Linke's uncompromising hard-left positions, such as wanting to abolish NATO and all secret services.
Germany's three leftist parties won combined support of under 40 per cent in last year's elections, which narrowly delivered a bruised Merkel, until then dubbed “the eternal chancellor”, her fourth four-year term.
The SPD was dispirited and split after a historically poor result, which forced it to reluctantly joined Merkel's conservatives again as junior partner, further damaging morale.
The working man's party, which saw mass desertions after the tough labour market reforms of previous chancellor Gerhard Schroeder, is now polling below 20 percent, raising existential angst.
The mood is more upbeat among the ecologist Greens, who under charismatic and pragmatic new co-leader Robert Habeck appear open to a future government alliance with either the SPD or conservatives.
Carsten Brzeski, chief economist with ING Diba bank, was doubtful about the future of “Stand Up”, after “Germany's left wing parties have failed to work together for decades”.
He said Stand Up appears “nationalist in tone, with anti-European and anti-refugee sentiments”.
“Such rhetoric not only plays on the under-currents running through society but is also a clear attempt to win back disappointed Linke voters in eastern Germany, who are now voting for the far-right AfD party,” he said.
“It's where the left and right meet.”