US Republican Greg Gianforte has won a special congressional election in Montana, just hours after he was charged with assaulting a UK reporter.
With about 96% of areas reporting, he has secured 51% of the vote. His Democratic rival Rob Quist has 43%.
Mr Gianforte has apologised for the incident in which he is accused of "body slamming" Ben Jacobs who works for the UK's Guardian newspaper.
In a victory speech he said he had "learned a lesson" and was "sorry".
A Fox News journalist who saw Wednesday's incident said Mr Gianforte had "grabbed Jacobs by the neck with both hands and slammed him into the ground" after the reporter persisted in trying to question him.
President Donald Trump praised the victory during an official trip to Italy, calling it a "great win in Montana".
Mr Gianforte had previously said Mr Jacobs had grabbed his wrist, pulling them both to the ground.
"When you make a mistake you have to own up to it, that's the Montana way," he said, after initial laughter among his supporters as he began to speak about the incident.
"Last night I made a mistake, I took an action that I can't take back.
"I am not proud of what happened, I should not have responded in the way that I did, and I'm sorry," he said.
"I should not have treated that reporter that way, and for that I'm sorry Mr Ben Jacobs," he added.
He has been charged with misdemeanour assault, for which the maximum penalty is a $500 (£385) fine and a six-month jail term.
Mr Gianforte, a multimillionaire technology executive and Christian conservative, beat Mr Quist, a banjo-playing folk singer, to fill an empty seat in the House of Representatives.
Mr Quist said he was "sure that Montanans will hold Mr Gianforte accountable."
The vacancy in Montana arose after President Trump appointed the previous holder of the seat, Ryan Zinke, as interior secretary.
Three of the state's largest newspapers withdrew their endorsements of Mr Gianforte after the violent incident on the eve of the vote.
The state's Democratic governor, Steve Bullock, described it as "a wake-up call to all Montanans and Americans".
"It is unsettling on many levels that Greg Gianforte physically assaulted a journalist and then lied, refusing to take responsibility for his actions," he said in a statement.
More than a third of the votes were cast by mail before it took place, an electoral official told Reuters.
Republicans have held the state's single seat in the House for two decades.
The party has, in general, been downplaying the case and casting it as an errant mistake, BBC North America reporter Anthony Zurcher says.
But critics are drawing the line between the rhetoric of President Trump - in which he has dubbed certain media outlets as "enemies of the American people" - and the incident, our correspondent adds.