Republican wins final unresolved US election race
US Representative Claudia Tenney and then president Donald Trump during a fundraiser for her failed re-election bid in August 2018 in Utica, New York (AFP)

The final unresolved race of the US election was brought to a conclusion Monday, three months after polling day and over a month since most lawmakers were sworn into Congress.

New York's elections board certified Republican Claudia Tenney as the winner of the state's 22nd congressional district over Democrat Anthony Brindisi.

She becomes the final member of the 435-seat lower chamber after months of wrangling over the vote count.

A judge on Friday ordered the New York State Board of Elections to certify a count that put Tenney just 109 votes ahead of Brindisi out of 300,000 ballots cast.

Brindisi, who had won the seat from Tenney in 2018, tweeted that he was "shocked," insisting that a "full audit and hand recount is the only way to resolve this race."

He had claimed there were problems with the way local authorities conducted the election, notably one county's failure to process 2,400 voting applications.

But the New York judge disagreed with him, and on Monday Brindisi conceded.

"It is time to close the book on this election and focus on building a better community and more united country for our children," Brindisi said in a statement.

The dispute was one of many legal battles that dogged the November 3 presidential and legislative elections after many voters cast ballots in advance or by mail due to the pandemic.

Former president Donald Trump and many Republicans alleged massive fraud, of which no evidence was found by multiple courts.

Most representatives were swore in to the 117th Congress by House speaker Nancy Pelosi on January 3, three days before a mob of Trump supporters stormed the US Capitol.

Democrats control the House by 221 to 210 Republicans before Tenney is sworn in.

They also control the US Senate under new President Joe Biden. The upper chamber is deadlocked at 50 members each but Vice President Kamala Harris enjoys a tie-breaking vote.