Quist, a popular 69-year-old singer and cowboy poet who was the front man for the Montana's Mission Mountain Wood Band, was helped by money that poured in from across the U.S.as Democrats seek to capture congressional seats that would have been considered safely Republican a year ago.
The Montana race focused on Quist's history of financial problems and Gianforte's stance on House Republicans' effort to dismantle Obamacare.
Jacobs said: "You just body-slammed me and broke my glasses".
Libertarian Mark Wicks had 6% the vote with 17,655 votes.
Gianforte used part of his victory to apologize to Guardian reporter Ben Jacobs.
Silver Sable And Black Cat nabs Beyond The Lights' Gina Prince-Bythewood
Sony is rebooting Spider-Man this summer with Spider-Man: Homecoming and hopes to launch a slate of Spider-Man-related movies. Palak Patel and Eric Fineman are overseeing " Silver Sable and Black Cat " for Columbia Pictures.
They said Gianforte also threw punches - an allegation that wasn't made by Jacobs or police.
Police were called to the scene of Wednesday's incident, at a Gianforte campaign event in the city of Bozeman, and Jacobs was taken to hospital for X-rays.
With 301,231 votes counted, Gianforte was up 50% to 44% with an edge of 151,021 votes to 132,555 for Quist, according to the Secretary of State website. "Not quirky personalities." Quist is a folk musician and first-time candidate. Some Republican lawmakers, including House Speaker Paul Ryan, suggested he apologise.
In his victory speech, Gianforte apologized to Jacobs. God Bless Montana and the United States of America.
While most Montana voters have already cast their ballots by mail, Bullock maintained that he hoped the incident would serve as a "wake-up call" for undecided voters who head to the polls today. "There's no question in my mind that Gianforte should not be sworn into office", Lujan said. Shaun Scott, a computer science professor at Carroll College in Helena, voted for Gianforte despite the assault charge because he felt Gianforte would do a better job helping create high technology jobs in Montana.
"There's never a time a physical altercation should occur with the press, or just between human beings", Mr Ryan told reporters Thursday in Washington. But whether those effects are enough to sway the outcome is a guessing game, he said. According to 538, there may have been a small shift toward Quist on election day, but it wasn't enough to make much of a difference.
Gianforte was projected the victor of Montana's special election just after midnight eastern time on Friday morning.
Republicans have held the state's single seat in the House for two decades. On Wednesday evening, he said he could not understand why the scuffle took place.