Despite the bruising election loss of his centre-left Social Democrats (SPD), he will now control the purse strings of Europe's top economy under conservative Chancellor Friedrich Merz.
Klingbeil -- who studied political science, sociology and history rather than finance -- will wield a spending "bazooka" worth hundreds of billions of euros to rebuild Germany's military and infrastructure, agreed by the previous parliament.
Having established a friendly rapport with political foe Merz during weeks of post-election coalition talks, he also serves as his vice chancellor, setting Klingbeil up for a potential future run at the top job himself.
Holding the powerful dual position at the tender age of 47 caps the career so far of a politician who favours dialogue and consensus over bluster and open power plays.
Klingbeil is "a politician who is ready to compromise, not an authoritarian leader who imposes his views on others", said political scientist Wolfgang Schroeder at the University of Kassel.
Der Spiegel magazine has described Klingbeil as "unflappable, unpretentious, unthreatening... almost boring."
He is someone who "weighs things up, thinks things through, and even slows things down when everyone else is convinced that a quick decision is necessary", it said.
It added that Klingbeil, who stands a towering 1.96 metres (6ft 5in) tall, "takes CrossFit and kickboxing classes several times a week, often before work, but then acts as if he couldn't hurt a fly".
Klingbeil states on his LinkedIn profile that he believes that "political compromises aren't inherently bad. I can say from my experience: building bridges is something I've always found enriching and something I can only encourage".
'Embrace your critics'
When Philipp Tuermer, head of the SPD's youth wing, laid into him over the coalition's plans to curb migration, Klingbeil defended the right of his young colleague to express a different opinion.
"That is the Klingbeil method: embrace your critics –- if in doubt, just about firmly enough that they no longer have room to move," Der Spiegel wrote.
Klingbeil was born in Soltau, near the northern city-state of Hamburg, and  lives in the same region with his wife, political scientist Lena-Sophie Mueller, and their infant, a boy born last summer.
As a youth, sporting an eyebrow piercing, Klingbeil was a member of a punk band and he still plays the guitar and reportedly keeps several of them in his office.
After performing civil service helping the homeless instead of military service, he went on to university.
He worked in the office of former SPD chancellor Gerhard Schroeder, from whom he has since distanced himself due Schroeder's links to Russian President Vladimir Putin.
Klingbeil first entered the Bundestag in 2005 and he served as the SPD's co-chair since 2021, together with Saskia Esken.
The SPD suffered the worst defeat in its history in February's election, winning just 16.4 percent of the vote.
After outgoing chancellor Olaf Scholz said he would take a back seat in coalition negotiations, Klingbeil became the SPD torch bearer, forging a congenial relationship with Merz.
Klingbeil is a Bayern Munich fan and a former member of the advisory board at Germany's biggest football club.
In recent weeks, Klingbeil, a former smoker, for the first time spoke publicly about being diagnosed with oral cancer in 2014, saying the ordeal had taught him to "approach things a bit more calmly".
"You look at life differently when you've had a brush with death," he told Die Zeit weekly.
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