The president stated that he would decide whether to run for a second term early next year.
Joe Biden has called his party’s positive midterm results a “good day for America,” but the Senate race remains tight.
Democrats are expected to lose only seven seats, defying predictions of a “giant red wave” of Republican gains.
Though the Republicans would retake control of the House of Representatives, this would be a far better outcome for the US president than his recent predecessors.
Donald Trump lost 40 seats in the 2018 midterms, while Barack Obama suffered 63 losses in 2010.
With three states left to declare, the battle for control of the Senate remains in the balance.
The Republicans have picked up 49 seats to the Democrats’ 48. The Republicans need to win two more seats to win back the Senate from the Democrats.
Speaking at the White House, President Biden described the midterm results so far as a “good day for democracy” and a “good day for America”.
Although many results are still unclear, he said they represent a “clear and unmistakable message to preserve our democracy”.
“The American people have spoken and shown that democracy is who we are,” he said.
But he added that “the voters were also clear that they’re still frustrated, I get it, it’s been a really tough few years for this country”.
In reference to Donald Trump‘s claims he “stole” the last elections, he said vote counters and officials “did their job and fulfilled their duty… without any interference”.
He also said he would make a decision on whether he would run for a second term early next year.
Although losing the House of Representatives would thwart the president’s legislative programme, it is a much smaller loss than some had predicted.
The race between Georgia’s incumbent Democrat senator and his Republican challenger is unlikely to be decided until 6 December, as strict state laws require a run-off if no candidate reaches 50%.
‘Democrats had strong night’
Mr Biden said the Democrats “had a strong night” despite losing seats.
“We don’t know all the results yet, but here’s what we do know, the press were predicting a giant red wave and it didn’t happen,” he said.
“You were somewhat miffed by my obsessive optimism, but I thought we were going to do fine.”
He said that the “future of America is too promising” for it to be “trapped in endless political warfare”.
While he would not compromise on healthcare or abortion, he said: “I’m going to do everything within my power to unite the country.
“I’m going to continue to work across the aisle to support the American people. Regardless of what the final tally of these elections show, I am prepared to work with my Republican colleagues.
“And the American people have made clear they expect Republicans to work with me as well.”
He addressed the nation after Donald Trump described his candidates’ results so far as “somewhat disappointing”.
Almost all the people Mr Trump chose to endorse appear to have fared worse than the Republicans he did not back.
Reports claim behind the scenes he is “livid” and “angry” at his wife Melania for advising him to back Dr Mehmet Oz in the Pennsylvania senate race.
Speaking from his Mar-a-Lago home, the former president claimed the results were a “very big victory” for him personally.