After first estimates showed the leftwing opposition winning Monday’s legislative elections, the dapper 61-year-old is expected to head a government whose parliamentary majority will be determined by negotiations with various parties in the days and weeks ahead.
Store campaigned against social inequalities in wealthy Norway, one of the most egalitarian countries in the OECD but which saw the number of billionaires more than double under the outgoing centre-right government.
“Now it’s the turn of the ordinary people,” he hammered throughout the campaign.
His crusade may seem odd for someone whose wealth has been estimated at 140 million kroner (around 14 millions euros, $16 million), and who is often knocked for having the “airs of a rightwinger”.
“My finances are not ordinary, but many things about me are,” he told AFP.
Married and the father of three, Store is an heir in several senses of the word.
His fortune comes from the sale of a family stove manufacturing company that was saved from bankruptcy by his grandfather.
He’s also a political heir, walking in the footsteps of his friend and mentor, former prime minister Jens Stoltenberg.
Store served as foreign minister in his government from 2005 to 2012, and health minister in 2012-2013.
When Stoltenberg was named the head of NATO in 2014, his protege Store was the natural choice to replace him as Labour Party leader.
Well, sort of natural. His arrival at the head of the party that traditionally represents workers did not sit very well with everybody.
His stellar education — Sciences Po in Paris, a brief stint at the London School of Economics and a research position at Harvard Law School — his millions, his technocrat elegance, and the fact that he speaks French all give him an elitist air that rubs some Norwegians the wrong way, especially those in the left-wing of his party.
As an editorialist once put it, Store has had to “climb the social ladder in reverse”.
The son of a shipbroker and a librarian, he takes care to fly the Norwegian flag for the international workers day on May 1, after being criticised for not doing so.
“He’s a political leader who people sometimes make fun of, an intellectual seen as being a little out of place in the Labour Party but he’s done well in this campaign,” political analyst Johannes Bergh said before the vote.
Almost everyone acknowledges his refined eloquence — though while some say it as a compliment others claim he uses it as a weapon to create ambiguity.
“Jonas is an extraordinary person,” Stoltenberg said when he handed over the reins of the party leadership to him.
“He knows a lot and has a huge workload capacity, which he combines with the gift of making the people around him happy.”
Fresh out of university, Store went to work for the “mother of the nation” Gro Harlem Brundtland as her advisor when she was prime minister and then head of the World Health Organization (WHO).
Working at the foreign ministry after a brief stint as the head of the Norwegian Red Cross, he earned the nickname “Super-Jonas” for all of his successes, though he has said he doesn’t really like the moniker.
Having made the Arctic one of his political priorities, he fostered closer ties with neighbouring Russia.
“I see him almost as often as I see my wife,” joked his Russian counterpart Sergei Lavrov.
In 2010, the two resolved a longstanding dispute over maritime borders, thereby opening up new waters in the Barents Sea to oil prospecting.
Store’s period as foreign minister was also one of drama.
In 2008, the Serena Hotel in Kabul where he was staying was attacked by the Taliban. Store was not hurt, having sought refuge in a saferoom, but six people were killed.
The politician was also one of rightwing extremist Anders Behring Breivik’s targets when he opened fire at a Labour youth gathering on the island of Utoya in July 2011.
Store had visited the island the day before.