In his acceptance speech, Gianforte apologized by name to Ben Jacobs, the Guardian reporter who accused the Republican of "body-slamming" him and breaking his glasses.
"When you make a mistake, you have to own up to it," Gianforte told his supporters at his Election Night rally in Bozeman. "That's the Montana way."
Saying he was "not proud" of his behavior, he added, "I should not have responded the way I did, for that I'm sorry. I should not have treated that reporter that way, and for that I'm sorry, Mr. Ben Jacobs."
With 87% of precincts reporting, Gianforte had 181,255 votes -- or 50.6% of the vote, compared to Quist who has 156,130 votes, 43.6% of the vote, according to Edison Research.
Gianforte was considered the favorite heading into Thursday's election to fill the seat once held by Interior Secretary Ryan Zinke, but that was before the altercation with Jacobs on Wednesday. The Gallatin County Sheriff's office later charged Gianforte with misdemeanor assault
The congressional race in Montana pitted two diametrically opposed candidates
against one another. Gianforte: an articulate millionaire and tech entrepreneur who sold his company RightNow Technologies to Oracle in 2012 for $1.8 billion. Quist: a first-time candidate and Montana folk singer who'd amassed moderate Montana fame in the 1970s as a member of the Mission Mountain Wood Band.
The early crowd of voters at Gianforte's rally were standing by the candidate, unfazed by the events of the previous 24 hours.
"We whole-heartedly support Greg. We love him," said Karen Screnar, a Republican voter who had driven all the way from Helena to support Gianforte. Screnar said she and her husband have known Gianforte for the better part of a decade. After Gianforte was charged with misdemeanor assault, Screnar said she was only "more ready to support Greg."
"We've watched how the press is one-sided. Excuse me, that's how I feel. (They're) making him their whipping boy so to speak through this campaign," Screaner said. "There comes a point where, stop it."
Her husband, Terry, chimed in that he believed Gianforte was "set up."
Meanwhile in Missoula, Quist who had a live band on stage at his rally, with some supporters dancing, a crowd made of young, college-aged voters as well as older liberal Missoulans.
The race seemed to be a longshot for Quist. In November, Trump won the state by 20 points and a Democrat hasn't won the congressional seat for two decades. In recent weeks, however, as Trump has grappled with his own controversies in Washington over the ongoing Russia investigation
, the race tightened.
Since Republicans in Congress passed a repeal of Obamacare earlier this month
, Quist had doubled down on his embrace of health care as a cornerstone of the campaign. Quist blamed a botched gallbladder surgery when confronted with a series of attacks that he had unpaid property taxes and debts.
This story has been updated and will be updated to reflect new developments.