Jon Tester claimed victory in his bid to defeat Matt Rosendale and Elinor Swanson.
The Senate race is the most expensive single electoral contest in Montana history, with more than $60 million spent by the candidates and outside groups.
Gianforte had 53 percent of the vote and a 35,000-vote lead over Williams, who had 45 percent.
As of 11:30 p.m. on Tuesday, many races across Montana are too close to call
The rally topics included economic reform, immigration, and control of the Supreme Court.
As of Monday morning, a record-high 303,000 Montanans had already voted by submitting absentee ballots through the mail
With less than a week until election day, campaign spending by outside groups on Montana’s U.S. Senate race has topped $33 million, easily breaking the old record for a Montana campaign.
Libertarian U.S. Senate candidate Rick Breckenridge on Wednesday threw his support behind Republican Matt Rosendale, in part because of what he and Rosendale called an illegal “dark money” mailer meant to help Democratic incumbent Jon Tester.
The opponents of Initiative 185, which would extend Montana’s Medicaid expansion, say the program that offers government-funded health coverage to nearly 100,000 low-income adults, will squeeze the state budget if it’s not revised.
Each candidate is getting about three-fourths of his campaign cash from outside Montana, according to an analysis by MTN News
MTN News has confirmed that President Trump will visit Bozeman before Election Day
The incident made national news again last week when President Trump, at a campaign rally in Missoula, joked about Gianforte assaulting Jacobs.
Since mid-May, the Gianforte campaign has slightly outspent Williams, $3.1 million to $2.66 million.
The poll has an error margin of plus-or-minus 2 percent.
Under current law, Montana’s Medicaid expansion is scheduled to expire next June 30.