"I was quite surprised [Obama was declared the winner so early]. If you'd asked me two weeks ago, I would have bet on Romney."
Obama had a slim 50 percent to 48 percent edge over Republican challenger Mitt Romney in the popular vote, but is projected to gain a decisive 303-206 victory in the all-important tally of electoral college votes.
Ullenhag was among several hundred attendees at an event organized by the US Embassy at a hotel in central Stockhlom, which was attended by several government ministers and MPs.
US ambassador Mark Brzezinski, who has served as Obama's envoy in Stockholm since October 2011, couldn't help but savour the moment that all but ensured his tenure in Stockholm would continue.
"Four years ago, I never would have imagined that I'd be here in Stockholm celebrating the US election," he told the assembled guests to rounds of applause shortly after Obama had been declared victorious by several US television networks.
"It is awesome to share this with our Swedish friends and our diplomat friends."
Social Democrat MP Thomas Östros, his party's former economic policy spokesman, also hailed Obama's re-election, calling it "well-deserved".
"It has been a tremendously difficult time with the economic downturn. It's going to be interesting to see what he can do with four years in a better economic environment," he told The Local.
Östros said Swedes and Europeans would likely react positively to Obama's second term in the White House, in part because of the values he represents.
"I think the election result when it comes to values is very important for Europe," he said.
"We've had an offensive period from right-wing conservatives and they have been defeated, and that will influence Europe; to see that modern values are winning in the US means a lot in Europe."
While Östros acknowledged that Obama will have a tough time addressing the Unites States' fiscal challenges, he expressed optimism that Americans' can-do spirit will prevail.
"I think it will be solved because Americans solve these sorts of issues. Late, perhaps, but they do do it," he said.
"Perhaps after this defeat there will also be some Republicans who are willing to be more reasonable."
Speaking on Sveriges Television (SVT), Prime Minister Fredrik Reinfeldt also touched on the economic challenges facing Obama in his second term.
"They have a huge debt and huge deficit. How they manage it will affect demand. This is a country that accounts for 20 percent of the world's demands for exports and it will affect China and Europe, and therefore Sweden," he said.
Reinfeldt also praised Obama for running a successful re-election campaign.
"He's been re-elected and has run a good and inclusive campaign. The Democrats are better at speaking to the whole of the United States," he said.
Social Democrat leader Stefan Löfven, meanwhile, hoped that the Democrats could afford to "have a real party" to celebrate the Obama win.
"When you look at Obama's campaign, you see there is a belief that politics and not just the market can make a difference," he told SVT.
Social Democrats also mentioned hopes that Obama would be more active in foreign policy, with Löfven saying he was "disappointed" with how the US president's Middle East policy during his first term.
Östros echoed similar sentiments.
"I hope that Obama can be a little bit bolder in foreign policy, particularly in the Middle East, now that he doesn't have to be worried about re-election," Östros told The Local.
Green Party spokeswoman Åsa Romson was also buoyant in her reaction to Obama's win.
"It's great news," she said in a statement.
"Barack Obama stands for a modern view on issues such as women's rights, migration, and security policy. He's a better representative for the diverse society that the United States is today."
Romson however expressed regret that climate issues were prioritized by Obama during his first term, urging him to "live up to the high expectations and take responsibility" for addressing global climate challenges.